diff --git a/ethcore/light/src/client/mod.rs b/ethcore/light/src/client/mod.rs
index 3f0e50584..d1cdfe9aa 100644
--- a/ethcore/light/src/client/mod.rs
+++ b/ethcore/light/src/client/mod.rs
@@ -100,8 +100,8 @@ pub trait LightChainClient: Send + Sync {
 	/// Get an iterator over a block and its ancestry.
 	fn ancestry_iter<'a>(&'a self, start: BlockId) -> Box<Iterator<Item=encoded::Header> + 'a>;
 
-	/// Get the signing network ID.
-	fn signing_network_id(&self) -> Option<u64>;
+	/// Get the signing chain ID.
+	fn signing_chain_id(&self) -> Option<u64>;
 
 	/// Get environment info for execution at a given block.
 	/// Fails if that block's header is not stored.
@@ -260,9 +260,9 @@ impl Client {
 		self.chain.ancestry_iter(start)
 	}
 
-	/// Get the signing network id.
-	pub fn signing_network_id(&self) -> Option<u64> {
-		self.engine.signing_network_id(&self.latest_env_info())
+	/// Get the signing chain id.
+	pub fn signing_chain_id(&self) -> Option<u64> {
+		self.engine.signing_chain_id(&self.latest_env_info())
 	}
 
 	/// Flush the header queue.
@@ -448,8 +448,8 @@ impl LightChainClient for Client {
 		Box::new(Client::ancestry_iter(self, start))
 	}
 
-	fn signing_network_id(&self) -> Option<u64> {
-		Client::signing_network_id(self)
+	fn signing_chain_id(&self) -> Option<u64> {
+		Client::signing_chain_id(self)
 	}
 
 	fn env_info(&self, id: BlockId) -> Option<EnvInfo> {
diff --git a/ethcore/src/client/client.rs b/ethcore/src/client/client.rs
index fdd201e68..edfb3c97c 100644
--- a/ethcore/src/client/client.rs
+++ b/ethcore/src/client/client.rs
@@ -1719,8 +1719,8 @@ impl BlockChainClient for Client {
 		}
 	}
 
-	fn signing_network_id(&self) -> Option<u64> {
-		self.engine.signing_network_id(&self.latest_env_info())
+	fn signing_chain_id(&self) -> Option<u64> {
+		self.engine.signing_chain_id(&self.latest_env_info())
 	}
 
 	fn block_extra_info(&self, id: BlockId) -> Option<BTreeMap<String, String>> {
@@ -1759,9 +1759,9 @@ impl BlockChainClient for Client {
 			value: U256::zero(),
 			data: data,
 		};
-		let network_id = self.engine.signing_network_id(&self.latest_env_info());
-		let signature = self.engine.sign(transaction.hash(network_id))?;
-		let signed = SignedTransaction::new(transaction.with_signature(signature, network_id))?;
+		let chain_id = self.engine.signing_chain_id(&self.latest_env_info());
+		let signature = self.engine.sign(transaction.hash(chain_id))?;
+		let signed = SignedTransaction::new(transaction.with_signature(signature, chain_id))?;
 		self.miner.import_own_transaction(self, signed.into())
 	}
 
diff --git a/ethcore/src/client/test_client.rs b/ethcore/src/client/test_client.rs
index 2a205868d..b6e0ba02e 100644
--- a/ethcore/src/client/test_client.rs
+++ b/ethcore/src/client/test_client.rs
@@ -733,7 +733,7 @@ impl BlockChainClient for TestBlockChainClient {
 		self.miner.ready_transactions(info.best_block_number, info.best_block_timestamp)
 	}
 
-	fn signing_network_id(&self) -> Option<u64> { None }
+	fn signing_chain_id(&self) -> Option<u64> { None }
 
 	fn mode(&self) -> Mode { Mode::Active }
 
@@ -764,9 +764,9 @@ impl BlockChainClient for TestBlockChainClient {
 			value: U256::default(),
 			data: data,
 		};
-		let network_id = Some(self.spec.params().network_id);
-		let sig = self.spec.engine.sign(transaction.hash(network_id)).unwrap();
-		let signed = SignedTransaction::new(transaction.with_signature(sig, network_id)).unwrap();
+		let chain_id = Some(self.spec.chain_id());
+		let sig = self.spec.engine.sign(transaction.hash(chain_id)).unwrap();
+		let signed = SignedTransaction::new(transaction.with_signature(sig, chain_id)).unwrap();
 		self.miner.import_own_transaction(self, signed.into())
 	}
 
diff --git a/ethcore/src/client/traits.rs b/ethcore/src/client/traits.rs
index 8e1bd8b18..40d2fab8e 100644
--- a/ethcore/src/client/traits.rs
+++ b/ethcore/src/client/traits.rs
@@ -239,8 +239,8 @@ pub trait BlockChainClient : Sync + Send {
 		corpus.into()
 	}
 
-	/// Get the preferred network ID to sign on
-	fn signing_network_id(&self) -> Option<u64>;
+	/// Get the preferred chain ID to sign on
+	fn signing_chain_id(&self) -> Option<u64>;
 
 	/// Get the mode.
 	fn mode(&self) -> Mode;
diff --git a/ethcore/src/engines/authority_round/mod.rs b/ethcore/src/engines/authority_round/mod.rs
index e7284bfbe..194fdd8fe 100644
--- a/ethcore/src/engines/authority_round/mod.rs
+++ b/ethcore/src/engines/authority_round/mod.rs
@@ -804,9 +804,9 @@ impl Engine for AuthorityRound {
 	fn verify_transaction_basic(&self, t: &UnverifiedTransaction, header: &Header) -> Result<(), Error> {
 		t.check_low_s()?;
 
-		if let Some(n) = t.network_id() {
+		if let Some(n) = t.chain_id() {
 			if header.number() >= self.params().eip155_transition && n != self.params().chain_id {
-				return Err(TransactionError::InvalidNetworkId.into());
+				return Err(TransactionError::InvalidChainId.into());
 			}
 		}
 
diff --git a/ethcore/src/engines/mod.rs b/ethcore/src/engines/mod.rs
index a293963d7..00f322318 100644
--- a/ethcore/src/engines/mod.rs
+++ b/ethcore/src/engines/mod.rs
@@ -263,7 +263,7 @@ pub trait Engine : Sync + Send {
 	// TODO: Add flags for which bits of the transaction to check.
 	// TODO: consider including State in the params.
 	fn verify_transaction_basic(&self, t: &UnverifiedTransaction, _header: &Header) -> Result<(), Error> {
-		t.verify_basic(true, Some(self.params().network_id), true)?;
+		t.verify_basic(true, Some(self.params().chain_id), true)?;
 		Ok(())
 	}
 
@@ -273,7 +273,7 @@ pub trait Engine : Sync + Send {
 	}
 
 	/// The network ID that transactions should be signed with.
-	fn signing_network_id(&self, _env_info: &EnvInfo) -> Option<u64> {
+	fn signing_chain_id(&self, _env_info: &EnvInfo) -> Option<u64> {
 		Some(self.params().chain_id)
 	}
 
diff --git a/ethcore/src/engines/validator_set/safe_contract.rs b/ethcore/src/engines/validator_set/safe_contract.rs
index 96790dca7..1abcf2c8f 100644
--- a/ethcore/src/engines/validator_set/safe_contract.rs
+++ b/ethcore/src/engines/validator_set/safe_contract.rs
@@ -452,7 +452,7 @@ mod tests {
 		let s0: Secret = "1".sha3().into();
 		let v0 = tap.insert_account(s0.clone(), "").unwrap();
 		let v1 = tap.insert_account("0".sha3().into(), "").unwrap();
-		let network_id = Spec::new_validator_safe_contract().network_id();
+		let chain_id = Spec::new_validator_safe_contract().chain_id();
 		let client = generate_dummy_client_with_spec_and_accounts(Spec::new_validator_safe_contract, Some(tap));
 		client.engine().register_client(Arc::downgrade(&client));
 		let validator_contract = "0000000000000000000000000000000000000005".parse::<Address>().unwrap();
@@ -466,7 +466,7 @@ mod tests {
 			action: Action::Call(validator_contract),
 			value: 0.into(),
 			data: "bfc708a000000000000000000000000082a978b3f5962a5b0957d9ee9eef472ee55b42f1".from_hex().unwrap(),
-		}.sign(&s0, Some(network_id));
+		}.sign(&s0, Some(chain_id));
 		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
 		client.update_sealing();
 		assert_eq!(client.chain_info().best_block_number, 1);
@@ -478,7 +478,7 @@ mod tests {
 			action: Action::Call(validator_contract),
 			value: 0.into(),
 			data: "4d238c8e00000000000000000000000082a978b3f5962a5b0957d9ee9eef472ee55b42f1".from_hex().unwrap(),
-		}.sign(&s0, Some(network_id));
+		}.sign(&s0, Some(chain_id));
 		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
 		client.update_sealing();
 		// The transaction is not yet included so still unable to seal.
@@ -497,7 +497,7 @@ mod tests {
 			action: Action::Call(Address::default()),
 			value: 0.into(),
 			data: Vec::new(),
-		}.sign(&s0, Some(network_id));
+		}.sign(&s0, Some(chain_id));
 		client.miner().import_own_transaction(client.as_ref(), tx.into()).unwrap();
 		client.update_sealing();
 		// Able to seal again.
diff --git a/ethcore/src/error.rs b/ethcore/src/error.rs
index 194cbcb38..172323c0d 100644
--- a/ethcore/src/error.rs
+++ b/ethcore/src/error.rs
@@ -78,8 +78,8 @@ pub enum TransactionError {
 	RecipientBanned,
 	/// Contract creation code is banned.
 	CodeBanned,
-	/// Invalid network ID given.
-	InvalidNetworkId,
+	/// Invalid chain ID given.
+	InvalidChainId,
 }
 
 impl fmt::Display for TransactionError {
@@ -103,7 +103,7 @@ impl fmt::Display for TransactionError {
 			SenderBanned => "Sender is temporarily banned.".into(),
 			RecipientBanned => "Recipient is temporarily banned.".into(),
 			CodeBanned => "Contract code is temporarily banned.".into(),
-			InvalidNetworkId => "Transaction of this network ID is not allowed on this chain.".into(),
+			InvalidChainId => "Transaction of this chain ID is not allowed on this chain.".into(),
 		};
 
 		f.write_fmt(format_args!("Transaction error ({})", msg))
diff --git a/ethcore/src/ethereum/ethash.rs b/ethcore/src/ethereum/ethash.rs
index 7e275cf98..adb1f7dac 100644
--- a/ethcore/src/ethereum/ethash.rs
+++ b/ethcore/src/ethereum/ethash.rs
@@ -206,7 +206,7 @@ impl Engine for Arc<Ethash> {
 		}
 	}
 
-	fn signing_network_id(&self, env_info: &EnvInfo) -> Option<u64> {
+	fn signing_chain_id(&self, env_info: &EnvInfo) -> Option<u64> {
 		if env_info.number >= self.params().eip155_transition {
 			Some(self.params().chain_id)
 		} else {
@@ -397,8 +397,8 @@ impl Engine for Arc<Ethash> {
 		}
 
 		let check_low_s = header.number() >= self.ethash_params.homestead_transition;
-		let network_id = if header.number() >= self.params().eip155_transition { Some(self.params().chain_id) } else { None };
-		t.verify_basic(check_low_s, network_id, false)?;
+		let chain_id = if header.number() >= self.params().eip155_transition { Some(self.params().chain_id) } else { None };
+		t.verify_basic(check_low_s, chain_id, false)?;
 		Ok(())
 	}
 
diff --git a/ethcore/src/json_tests/transaction.rs b/ethcore/src/json_tests/transaction.rs
index a3c3c889d..3d71a5faf 100644
--- a/ethcore/src/json_tests/transaction.rs
+++ b/ethcore/src/json_tests/transaction.rs
@@ -36,25 +36,25 @@ fn do_json_test(json_data: &[u8]) -> Vec<String> {
 			Some(x) if x < 3_000_000 => &homestead_schedule,
 			Some(_) => &metropolis_schedule
 		};
-		let allow_network_id_of_one = number.map_or(false, |n| n >= 2_675_000);
+		let allow_chain_id_of_one = number.map_or(false, |n| n >= 2_675_000);
 		let allow_unsigned = number.map_or(false, |n| n >= 3_000_000);
 
 		let rlp: Vec<u8> = test.rlp.into();
 		let res = UntrustedRlp::new(&rlp)
 			.as_val()
 			.map_err(From::from)
-			.and_then(|t: UnverifiedTransaction| t.validate(schedule, schedule.have_delegate_call, allow_network_id_of_one, allow_unsigned));
+			.and_then(|t: UnverifiedTransaction| t.validate(schedule, schedule.have_delegate_call, allow_chain_id_of_one, allow_unsigned));
 
 		fail_unless(test.transaction.is_none() == res.is_err(), "Validity different");
 		if let (Some(tx), Some(sender)) = (test.transaction, test.sender) {
 			let t = res.unwrap();
 			fail_unless(SignedTransaction::new(t.clone()).unwrap().sender() == sender.into(), "sender mismatch");
-			let is_acceptable_network_id = match t.network_id() {
+			let is_acceptable_chain_id = match t.chain_id() {
 				None => true,
-				Some(1) if allow_network_id_of_one => true,
+				Some(1) if allow_chain_id_of_one => true,
 				_ => false,
 			};
-			fail_unless(is_acceptable_network_id, "Network ID unacceptable");
+			fail_unless(is_acceptable_chain_id, "Network ID unacceptable");
 			let data: Vec<u8> = tx.data.into();
 			fail_unless(t.data == data, "data mismatch");
 			fail_unless(t.gas_price == tx.gas_price.into(), "gas_price mismatch");
diff --git a/ethcore/src/miner/miner.rs b/ethcore/src/miner/miner.rs
index 02463d929..0639c645f 100644
--- a/ethcore/src/miner/miner.rs
+++ b/ethcore/src/miner/miner.rs
@@ -1306,10 +1306,10 @@ mod tests {
 	}
 
 	fn transaction() -> SignedTransaction {
-		transaction_with_network_id(2)
+		transaction_with_chain_id(2)
 	}
 
-	fn transaction_with_network_id(id: u64) -> SignedTransaction {
+	fn transaction_with_chain_id(chain_id: u64) -> SignedTransaction {
 		let keypair = Random.generate().unwrap();
 		Transaction {
 			action: Action::Create,
@@ -1318,7 +1318,7 @@ mod tests {
 			gas: U256::from(100_000),
 			gas_price: U256::zero(),
 			nonce: U256::zero(),
-		}.sign(keypair.secret(), Some(id))
+		}.sign(keypair.secret(), Some(chain_id))
 	}
 
 	#[test]
@@ -1399,14 +1399,14 @@ mod tests {
 
 		let client = generate_dummy_client(2);
 
-		assert_eq!(miner.import_external_transactions(&*client, vec![transaction_with_network_id(spec.network_id()).into()]).pop().unwrap().unwrap(), TransactionImportResult::Current);
+		assert_eq!(miner.import_external_transactions(&*client, vec![transaction_with_chain_id(spec.chain_id()).into()]).pop().unwrap().unwrap(), TransactionImportResult::Current);
 
 		miner.update_sealing(&*client);
 		client.flush_queue();
 		assert!(miner.pending_block(0).is_none());
 		assert_eq!(client.chain_info().best_block_number, 3 as BlockNumber);
 
-		assert_eq!(miner.import_own_transaction(&*client, PendingTransaction::new(transaction_with_network_id(spec.network_id()).into(), None)).unwrap(), TransactionImportResult::Current);
+		assert_eq!(miner.import_own_transaction(&*client, PendingTransaction::new(transaction_with_chain_id(spec.chain_id()).into(), None)).unwrap(), TransactionImportResult::Current);
 
 		miner.update_sealing(&*client);
 		client.flush_queue();
diff --git a/ethcore/src/snapshot/tests/proof_of_authority.rs b/ethcore/src/snapshot/tests/proof_of_authority.rs
index a62dbaf10..7c44ec20a 100644
--- a/ethcore/src/snapshot/tests/proof_of_authority.rs
+++ b/ethcore/src/snapshot/tests/proof_of_authority.rs
@@ -130,7 +130,7 @@ fn make_chain(accounts: Arc<AccountProvider>, blocks_beyond: usize, transitions:
 				action: Action::Call(Address::new()),
 				value: 1.into(),
 				data: Vec::new(),
-			}.sign(&*RICH_SECRET, client.signing_network_id());
+			}.sign(&*RICH_SECRET, client.signing_chain_id());
 
 			*nonce = *nonce + 1.into();
 			vec![transaction]
@@ -176,7 +176,7 @@ fn make_chain(accounts: Arc<AccountProvider>, blocks_beyond: usize, transitions:
 							action: Action::Call(addr),
 							value: 0.into(),
 							data: data,
-						}.sign(&*RICH_SECRET, client.signing_network_id());
+						}.sign(&*RICH_SECRET, client.signing_chain_id());
 
 						pending.push(transaction);
 
diff --git a/ethcore/src/spec/spec.rs b/ethcore/src/spec/spec.rs
index 395f8ef9c..ba57a7f27 100644
--- a/ethcore/src/spec/spec.rs
+++ b/ethcore/src/spec/spec.rs
@@ -380,6 +380,9 @@ impl Spec {
 	/// Get the configured Network ID.
 	pub fn network_id(&self) -> u64 { self.params().network_id }
 
+	/// Get the chain ID used for signing.
+	pub fn chain_id(&self) -> u64 { self.params().chain_id }
+
 	/// Get the configured subprotocol name.
 	pub fn subprotocol_name(&self) -> String { self.params().subprotocol_name.clone() }
 
diff --git a/ethcore/src/tests/helpers.rs b/ethcore/src/tests/helpers.rs
index 5d05e66f5..d8ba8313e 100644
--- a/ethcore/src/tests/helpers.rs
+++ b/ethcore/src/tests/helpers.rs
@@ -211,7 +211,7 @@ pub fn generate_dummy_client_with_spec_accounts_and_data<F>(get_test_spec: F, ac
 				action: Action::Create,
 				data: vec![],
 				value: U256::zero(),
-			}.sign(kp.secret(), Some(test_spec.network_id())), None).unwrap();
+			}.sign(kp.secret(), Some(test_spec.chain_id())), None).unwrap();
 			n += 1;
 		}
 
diff --git a/ethcore/src/transaction.rs b/ethcore/src/transaction.rs
index 2752cc6dd..0bd61dceb 100644
--- a/ethcore/src/transaction.rs
+++ b/ethcore/src/transaction.rs
@@ -94,15 +94,15 @@ pub struct Transaction {
 
 impl Transaction {
 	/// Append object with a without signature into RLP stream
-	pub fn rlp_append_unsigned_transaction(&self, s: &mut RlpStream, network_id: Option<u64>) {
-		s.begin_list(if network_id.is_none() { 6 } else { 9 });
+	pub fn rlp_append_unsigned_transaction(&self, s: &mut RlpStream, chain_id: Option<u64>) {
+		s.begin_list(if chain_id.is_none() { 6 } else { 9 });
 		s.append(&self.nonce);
 		s.append(&self.gas_price);
 		s.append(&self.gas);
 		s.append(&self.action);
 		s.append(&self.value);
 		s.append(&self.data);
-		if let Some(n) = network_id {
+		if let Some(n) = chain_id {
 			s.append(&n);
 			s.append(&0u8);
 			s.append(&0u8);
@@ -163,27 +163,27 @@ impl From<ethjson::transaction::Transaction> for UnverifiedTransaction {
 
 impl Transaction {
 	/// The message hash of the transaction.
-	pub fn hash(&self, network_id: Option<u64>) -> H256 {
+	pub fn hash(&self, chain_id: Option<u64>) -> H256 {
 		let mut stream = RlpStream::new();
-		self.rlp_append_unsigned_transaction(&mut stream, network_id);
+		self.rlp_append_unsigned_transaction(&mut stream, chain_id);
 		stream.as_raw().sha3()
 	}
 
 	/// Signs the transaction as coming from `sender`.
-	pub fn sign(self, secret: &Secret, network_id: Option<u64>) -> SignedTransaction {
-		let sig = ::ethkey::sign(secret, &self.hash(network_id))
+	pub fn sign(self, secret: &Secret, chain_id: Option<u64>) -> SignedTransaction {
+		let sig = ::ethkey::sign(secret, &self.hash(chain_id))
 			.expect("data is valid and context has signing capabilities; qed");
-		SignedTransaction::new(self.with_signature(sig, network_id))
+		SignedTransaction::new(self.with_signature(sig, chain_id))
 			.expect("secret is valid so it's recoverable")
 	}
 
 	/// Signs the transaction with signature.
-	pub fn with_signature(self, sig: Signature, network_id: Option<u64>) -> UnverifiedTransaction {
+	pub fn with_signature(self, sig: Signature, chain_id: Option<u64>) -> UnverifiedTransaction {
 		UnverifiedTransaction {
 			unsigned: self,
 			r: sig.r().into(),
 			s: sig.s().into(),
-			v: sig.v() as u64 + if let Some(n) = network_id { 35 + n * 2 } else { 27 },
+			v: sig.v() as u64 + if let Some(n) = chain_id { 35 + n * 2 } else { 27 },
 			hash: 0.into(),
 		}.compute_hash()
 	}
@@ -216,13 +216,13 @@ impl Transaction {
 	}
 
 	/// Add EIP-86 compatible empty signature.
-	pub fn null_sign(self, network_id: u64) -> SignedTransaction {
+	pub fn null_sign(self, chain_id: u64) -> SignedTransaction {
 		SignedTransaction {
 			transaction: UnverifiedTransaction {
 				unsigned: self,
 				r: U256::zero(),
 				s: U256::zero(),
-				v: network_id,
+				v: chain_id,
 				hash: 0.into(),
 			}.compute_hash(),
 			sender: UNSIGNED_SENDER,
@@ -250,7 +250,7 @@ pub struct UnverifiedTransaction {
 	/// Plain Transaction.
 	unsigned: Transaction,
 	/// The V field of the signature; the LS bit described which half of the curve our point falls
-	/// in. The MS bits describe which network this transaction is for. If 27/28, its for all networks.
+	/// in. The MS bits describe which chain this transaction is for. If 27/28, its for all chains.
 	v: u64,
 	/// The R field of the signature; helps describe the point on the curve.
 	r: U256,
@@ -333,8 +333,8 @@ impl UnverifiedTransaction {
 	/// The `v` value that appears in the RLP.
 	pub fn original_v(&self) -> u64 { self.v }
 
-	/// The network ID, or `None` if this is a global transaction.
-	pub fn network_id(&self) -> Option<u64> {
+	/// The chain ID, or `None` if this is a global transaction.
+	pub fn chain_id(&self) -> Option<u64> {
 		match self.v {
 			v if self.is_unsigned() => Some(v),
 			v if v > 36 => Some((v - 35) / 2),
@@ -363,15 +363,15 @@ impl UnverifiedTransaction {
 
 	/// Recovers the public key of the sender.
 	pub fn recover_public(&self) -> Result<Public, Error> {
-		Ok(recover(&self.signature(), &self.unsigned.hash(self.network_id()))?)
+		Ok(recover(&self.signature(), &self.unsigned.hash(self.chain_id()))?)
 	}
 
 	/// Do basic validation, checking for valid signature and minimum gas,
 	// TODO: consider use in block validation.
 	#[cfg(test)]
 	#[cfg(feature = "json-tests")]
-	pub fn validate(self, schedule: &Schedule, require_low: bool, allow_network_id_of_one: bool, allow_empty_signature: bool) -> Result<UnverifiedTransaction, Error> {
-		let chain_id = if allow_network_id_of_one { Some(1) } else { None };
+	pub fn validate(self, schedule: &Schedule, require_low: bool, allow_chain_id_of_one: bool, allow_empty_signature: bool) -> Result<UnverifiedTransaction, Error> {
+		let chain_id = if allow_chain_id_of_one { Some(1) } else { None };
 		self.verify_basic(require_low, chain_id, allow_empty_signature)?;
 		if !allow_empty_signature || !self.is_unsigned() {
 			self.recover_public()?;
@@ -391,10 +391,10 @@ impl UnverifiedTransaction {
 		if allow_empty_signature && self.is_unsigned() && !(self.gas_price.is_zero() && self.value.is_zero() && self.nonce.is_zero()) {
 			return Err(EthkeyError::InvalidSignature.into())
 		}
-		match (self.network_id(), chain_id) {
+		match (self.chain_id(), chain_id) {
 			(None, _) => {},
 			(Some(n), Some(m)) if n == m => {},
-			_ => return Err(TransactionError::InvalidNetworkId.into()),
+			_ => return Err(TransactionError::InvalidChainId.into()),
 		};
 		Ok(())
 	}
@@ -558,7 +558,7 @@ mod tests {
 		} else { panic!(); }
 		assert_eq!(t.value, U256::from(0x0au64));
 		assert_eq!(public_to_address(&t.recover_public().unwrap()), "0f65fe9276bc9a24ae7083ae28e2660ef72df99e".into());
-		assert_eq!(t.network_id(), None);
+		assert_eq!(t.chain_id(), None);
 	}
 
 	#[test]
@@ -575,7 +575,7 @@ mod tests {
 			data: b"Hello!".to_vec()
 		}.sign(&key.secret(), None);
 		assert_eq!(Address::from(key.public().sha3()), t.sender());
-		assert_eq!(t.network_id(), None);
+		assert_eq!(t.chain_id(), None);
 	}
 
 	#[test]
@@ -589,15 +589,15 @@ mod tests {
 			data: b"Hello!".to_vec()
 		}.fake_sign(Address::from(0x69));
 		assert_eq!(Address::from(0x69), t.sender());
-		assert_eq!(t.network_id(), None);
+		assert_eq!(t.chain_id(), None);
 
 		let t = t.clone();
 		assert_eq!(Address::from(0x69), t.sender());
-		assert_eq!(t.network_id(), None);
+		assert_eq!(t.chain_id(), None);
 	}
 
 	#[test]
-	fn should_recover_from_network_specific_signing() {
+	fn should_recover_from_chain_specific_signing() {
 		use ethkey::{Random, Generator};
 		let key = Random.generate().unwrap();
 		let t = Transaction {
@@ -609,7 +609,7 @@ mod tests {
 			data: b"Hello!".to_vec()
 		}.sign(&key.secret(), Some(69));
 		assert_eq!(Address::from(key.public().sha3()), t.sender());
-		assert_eq!(t.network_id(), Some(69));
+		assert_eq!(t.chain_id(), Some(69));
 	}
 
 	#[test]
@@ -620,7 +620,7 @@ mod tests {
 			let signed = decode(&FromHex::from_hex(tx_data).unwrap());
 			let signed = SignedTransaction::new(signed).unwrap();
 			assert_eq!(signed.sender(), address.into());
-			flushln!("networkid: {:?}", signed.network_id());
+			flushln!("chainid: {:?}", signed.chain_id());
 		};
 
 		test_vector("f864808504a817c800825208943535353535353535353535353535353535353535808025a0044852b2a670ade5407e78fb2863c51de9fcb96542a07186fe3aeda6bb8a116da0044852b2a670ade5407e78fb2863c51de9fcb96542a07186fe3aeda6bb8a116d", "0xf0f6f18bca1b28cd68e4357452947e021241e9ce");
diff --git a/js/src/jsonrpc/interfaces/eth.js b/js/src/jsonrpc/interfaces/eth.js
index d54c57325..30756e8c6 100644
--- a/js/src/jsonrpc/interfaces/eth.js
+++ b/js/src/jsonrpc/interfaces/eth.js
@@ -566,9 +566,9 @@ The following options are possible for the \`defaultBlock\` parameter:
           type: Hash,
           desc: 'public key of the signer.'
         },
-        networkId: {
+        chainId: {
           type: Quantity,
-          desc: 'the network id of the transaction, if any.'
+          desc: 'the chain id of the transaction, if any.'
         },
         creates: {
           type: Hash,
@@ -1111,9 +1111,9 @@ The following options are possible for the \`defaultBlock\` parameter:
               type: Hash,
               desc: 'public key of the signer.'
             },
-            networkId: {
+            chainId: {
               type: Quantity,
-              desc: 'the network id of the transaction, if any.'
+              desc: 'the chain id of the transaction, if any.'
             },
             creates: {
               type: Hash,
diff --git a/js/src/jsonrpc/interfaces/parity.js b/js/src/jsonrpc/interfaces/parity.js
index d80a0c5a2..a1e6246e4 100644
--- a/js/src/jsonrpc/interfaces/parity.js
+++ b/js/src/jsonrpc/interfaces/parity.js
@@ -403,7 +403,7 @@ export default {
             condition: {
               block: 1
             },
-            networkId: null,
+            chainId: null,
             nonce: '0x0',
             publicKey: '0x3fa8c08c65a83f6b4ea3e04e1cc70cbe3cd391499e3e05ab7dedf28aff9afc538200ff93e3f2b2cb5029f03c7ebee820d63a4c5a9541c83acebe293f54cacf0e',
             raw: '0xf868808502d20cff33830e57e09400a289b43e1e4825dbedf2a78ba60a640634dc40830fffff801ca034c333b0b91cd832a3414d628e3fea29a00055cebf5ba59f7038c188404c0cf3a0524fd9b35be170439b5ffe89694ae0cfc553cb49d1d8b643239e353351531532',
@@ -626,7 +626,7 @@ export default {
           condition: {
             block: 1
           },
-          networkId: 1,
+          chainId: 1,
           nonce: '0x5',
           publicKey: '0x96157302dade55a1178581333e57d60ffe6fdf5a99607890456a578b4e6b60e335037d61ed58aa4180f9fd747dc50d44a7924aa026acbfb988b5062b629d6c36',
           r: '0x92e8beb19af2bad0511d516a86e77fa73004c0811b2173657a55797bdf8558e1',
@@ -688,7 +688,7 @@ export default {
           condition: {
             block: 1
           },
-          networkId: 1,
+          chainId: 1,
           nonce: '0x5',
           publicKey: '0x96157302dade55a1178581333e57d60ffe6fdf5a99607890456a578b4e6b60e335037d61ed58aa4180f9fd747dc50d44a7924aa026acbfb988b5062b629d6c36',
           r: '0x92e8beb19af2bad0511d516a86e77fa73004c0811b2173657a55797bdf8558e1',
@@ -980,7 +980,7 @@ export default {
           creates: null,
           raw: '0xf86c018504a817c80082520894f5d405530dabfbd0c1cab7a5812f008aa5559adf882efc004ac03a49968025a0b40c6967a7e8bbdfd99a25fd306b9ef23b80e719514aeb7ddd19e2303d6fc139a06bf770ab08119e67dc29817e1412a0e3086f43da308c314db1b3bca9fb6d32bd',
           publicKey: '0xeba33fd74f06236e17475bc5b6d1bac718eac048350d77d3fc8fbcbd85782a57c821255623c4fd1ebc9d555d07df453b2579ee557b7203fc256ca3b3401e4027',
-          networkId: 1,
+          chainId: 1,
           standardV: '0x0',
           v: '0x25',
           r: '0xb40c6967a7e8bbdfd99a25fd306b9ef23b80e719514aeb7ddd19e2303d6fc139',
diff --git a/js/src/jsonrpc/types.js b/js/src/jsonrpc/types.js
index c750932c9..bd69cc863 100644
--- a/js/src/jsonrpc/types.js
+++ b/js/src/jsonrpc/types.js
@@ -173,9 +173,9 @@ export class TransactionResponse {
       type: Data,
       desc: 'Public key of the signer.'
     },
-    networkId: {
+    chainId: {
       type: Quantity,
-      desc: 'The network id of the transaction, if any.'
+      desc: 'The chain id of the transaction, if any.'
     },
     standardV: {
       type: Quantity,
diff --git a/rpc/src/v1/helpers/dispatch.rs b/rpc/src/v1/helpers/dispatch.rs
index c72f1a890..b2602d6a1 100644
--- a/rpc/src/v1/helpers/dispatch.rs
+++ b/rpc/src/v1/helpers/dispatch.rs
@@ -133,7 +133,7 @@ impl<C: MiningBlockChainClient, M: MinerService> Dispatcher for FullDispatcher<C
 		-> BoxFuture<WithToken<SignedTransaction>, Error>
 	{
 		let (client, miner) = (self.client.clone(), self.miner.clone());
-		let network_id = client.signing_network_id();
+		let chain_id = client.signing_chain_id();
 		let address = filled.from;
 		future::done({
 			let t = Transaction {
@@ -146,12 +146,12 @@ impl<C: MiningBlockChainClient, M: MinerService> Dispatcher for FullDispatcher<C
 			};
 
 			if accounts.is_hardware_address(address) {
-				hardware_signature(&*accounts, address, t, network_id).map(WithToken::No)
+				hardware_signature(&*accounts, address, t, chain_id).map(WithToken::No)
 			} else {
-				let hash = t.hash(network_id);
+				let hash = t.hash(chain_id);
 				let signature = try_bf!(signature(&*accounts, address, hash, password));
 				Ok(signature.map(|sig| {
-					SignedTransaction::new(t.with_signature(sig, network_id))
+					SignedTransaction::new(t.with_signature(sig, chain_id))
 						.expect("Transaction was signed by AccountsProvider; it never produces invalid signatures; qed")
 				}))
 			}
@@ -358,7 +358,7 @@ impl Dispatcher for LightDispatcher {
 	fn sign(&self, accounts: Arc<AccountProvider>, filled: FilledTransactionRequest, password: SignWith)
 		-> BoxFuture<WithToken<SignedTransaction>, Error>
 	{
-		let network_id = self.client.signing_network_id();
+		let chain_id = self.client.signing_chain_id();
 		let address = filled.from;
 
 		let with_nonce = move |filled: FilledTransactionRequest, nonce| {
@@ -372,14 +372,14 @@ impl Dispatcher for LightDispatcher {
 			};
 
 			if accounts.is_hardware_address(address) {
-				return hardware_signature(&*accounts, address, t, network_id).map(WithToken::No)
+				return hardware_signature(&*accounts, address, t, chain_id).map(WithToken::No)
 			}
 
-			let hash = t.hash(network_id);
+			let hash = t.hash(chain_id);
 			let signature = signature(&*accounts, address, hash, password)?;
 
 			Ok(signature.map(|sig| {
-				SignedTransaction::new(t.with_signature(sig, network_id))
+				SignedTransaction::new(t.with_signature(sig, chain_id))
 					.expect("Transaction was signed by AccountsProvider; it never produces invalid signatures; qed")
 			}))
 		};
@@ -552,20 +552,20 @@ fn signature(accounts: &AccountProvider, address: Address, hash: H256, password:
 }
 
 // obtain a hardware signature from the given account.
-fn hardware_signature(accounts: &AccountProvider, address: Address, t: Transaction, network_id: Option<u64>)
+fn hardware_signature(accounts: &AccountProvider, address: Address, t: Transaction, chain_id: Option<u64>)
 	-> Result<SignedTransaction, Error>
 {
 	debug_assert!(accounts.is_hardware_address(address));
 
 	let mut stream = rlp::RlpStream::new();
-	t.rlp_append_unsigned_transaction(&mut stream, network_id);
+	t.rlp_append_unsigned_transaction(&mut stream, chain_id);
 	let signature = accounts.sign_with_hardware(address, &stream.as_raw())
 		.map_err(|e| {
 			debug!(target: "miner", "Error signing transaction with hardware wallet: {}", e);
 			errors::account("Error signing transaction with hardware wallet", e)
 		})?;
 
-	SignedTransaction::new(t.with_signature(signature, network_id))
+	SignedTransaction::new(t.with_signature(signature, chain_id))
 		.map_err(|e| {
 		  debug!(target: "miner", "Hardware wallet has produced invalid signature: {}", e);
 		  errors::account("Invalid signature generated", e)
diff --git a/rpc/src/v1/helpers/errors.rs b/rpc/src/v1/helpers/errors.rs
index 4c4af6f97..559f3a6b9 100644
--- a/rpc/src/v1/helpers/errors.rs
+++ b/rpc/src/v1/helpers/errors.rs
@@ -310,7 +310,7 @@ pub fn transaction_message(error: TransactionError) -> String {
 		GasLimitExceeded { limit, got } => {
 			format!("Transaction cost exceeds current gas limit. Limit: {}, got: {}. Try decreasing supplied gas.", limit, got)
 		},
-		InvalidNetworkId => "Invalid network id.".into(),
+		InvalidChainId => "Invalid chain id.".into(),
 		InvalidGasLimit(_) => "Supplied gas is beyond limit.".into(),
 		SenderBanned => "Sender is banned in local queue.".into(),
 		RecipientBanned => "Recipient is banned in local queue.".into(),
diff --git a/rpc/src/v1/impls/personal.rs b/rpc/src/v1/impls/personal.rs
index 8028168fd..302190fd4 100644
--- a/rpc/src/v1/impls/personal.rs
+++ b/rpc/src/v1/impls/personal.rs
@@ -124,9 +124,9 @@ impl<D: Dispatcher + 'static> Personal for PersonalClient<D> {
 					.map(move |tx| (tx, dispatcher))
 			})
 			.and_then(|(pending_tx, dispatcher)| {
-				let network_id = pending_tx.network_id();
-				trace!(target: "miner", "send_transaction: dispatching tx: {} for network ID {:?}",
-					::rlp::encode(&*pending_tx).into_vec().pretty(), network_id);
+				let chain_id = pending_tx.chain_id();
+				trace!(target: "miner", "send_transaction: dispatching tx: {} for chain ID {:?}",
+					::rlp::encode(&*pending_tx).into_vec().pretty(), chain_id);
 
 				dispatcher.dispatch_transaction(pending_tx).map(Into::into)
 			})
diff --git a/rpc/src/v1/tests/mocked/eth.rs b/rpc/src/v1/tests/mocked/eth.rs
index f935b93e2..d1835948f 100644
--- a/rpc/src/v1/tests/mocked/eth.rs
+++ b/rpc/src/v1/tests/mocked/eth.rs
@@ -544,7 +544,7 @@ fn rpc_eth_pending_transaction_by_hash() {
 		tester.miner.pending_transactions.lock().insert(H256::zero(), tx);
 	}
 
-	let response = r#"{"jsonrpc":"2.0","result":{"blockHash":null,"blockNumber":null,"condition":null,"creates":null,"from":"0x0f65fe9276bc9a24ae7083ae28e2660ef72df99e","gas":"0x5208","gasPrice":"0x1","hash":"0x41df922fd0d4766fcc02e161f8295ec28522f329ae487f14d811e4b64c8d6e31","input":"0x","networkId":null,"nonce":"0x0","publicKey":"0x7ae46da747962c2ee46825839c1ef9298e3bd2e70ca2938495c3693a485ec3eaa8f196327881090ff64cf4fbb0a48485d4f83098e189ed3b7a87d5941b59f789","r":"0x48b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353","raw":"0xf85f800182520894095e7baea6a6c7c4c2dfeb977efac326af552d870a801ba048b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353a0efffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c804","s":"0xefffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c804","standardV":"0x0","to":"0x095e7baea6a6c7c4c2dfeb977efac326af552d87","transactionIndex":null,"v":"0x1b","value":"0xa"},"id":1}"#;
+	let response = r#"{"jsonrpc":"2.0","result":{"blockHash":null,"blockNumber":null,"chainId":null,"condition":null,"creates":null,"from":"0x0f65fe9276bc9a24ae7083ae28e2660ef72df99e","gas":"0x5208","gasPrice":"0x1","hash":"0x41df922fd0d4766fcc02e161f8295ec28522f329ae487f14d811e4b64c8d6e31","input":"0x","nonce":"0x0","publicKey":"0x7ae46da747962c2ee46825839c1ef9298e3bd2e70ca2938495c3693a485ec3eaa8f196327881090ff64cf4fbb0a48485d4f83098e189ed3b7a87d5941b59f789","r":"0x48b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353","raw":"0xf85f800182520894095e7baea6a6c7c4c2dfeb977efac326af552d870a801ba048b55bfa915ac795c431978d8a6a992b628d557da5ff759b307d495a36649353a0efffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c804","s":"0xefffd310ac743f371de3b9f7f9cb56c0b28ad43601b4ab949f53faa07bd2c804","standardV":"0x0","to":"0x095e7baea6a6c7c4c2dfeb977efac326af552d87","transactionIndex":null,"v":"0x1b","value":"0xa"},"id":1}"#;
 	let request = r#"{
 		"jsonrpc": "2.0",
 		"method": "eth_getTransactionByHash",
@@ -860,12 +860,13 @@ fn rpc_eth_sign_transaction() {
 	let response = r#"{"jsonrpc":"2.0","result":{"#.to_owned() +
 		r#""raw":"0x"# + &rlp.to_hex() + r#"","# +
 		r#""tx":{"# +
-		r#""blockHash":null,"blockNumber":null,"condition":null,"creates":null,"# +
+		r#""blockHash":null,"blockNumber":null,"# +
+		&format!("\"chainId\":{},", t.chain_id().map_or("null".to_owned(), |n| format!("{}", n))) +
+		r#""condition":null,"creates":null,"# +
 		&format!("\"from\":\"0x{:?}\",", &address) +
 		r#""gas":"0x76c0","gasPrice":"0x9184e72a000","# +
 		&format!("\"hash\":\"0x{:?}\",", t.hash()) +
 		r#""input":"0x","# +
-		&format!("\"networkId\":{},", t.network_id().map_or("null".to_owned(), |n| format!("{}", n))) +
 		r#""nonce":"0x1","# +
 		&format!("\"publicKey\":\"0x{:?}\",", t.recover_public().unwrap()) +
 		&format!("\"r\":\"0x{}\",", U256::from(signature.r()).to_hex()) +
diff --git a/rpc/src/v1/tests/mocked/parity_set.rs b/rpc/src/v1/tests/mocked/parity_set.rs
index 443379b4f..22e0388e2 100644
--- a/rpc/src/v1/tests/mocked/parity_set.rs
+++ b/rpc/src/v1/tests/mocked/parity_set.rs
@@ -233,7 +233,7 @@ fn rpc_parity_remove_transaction() {
 	let hash = signed.hash();
 
 	let request = r#"{"jsonrpc": "2.0", "method": "parity_removeTransaction", "params":[""#.to_owned() + &format!("0x{:?}", hash) + r#""], "id": 1}"#;
-	let response = r#"{"jsonrpc":"2.0","result":{"blockHash":null,"blockNumber":null,"condition":null,"creates":null,"from":"0x0000000000000000000000000000000000000002","gas":"0x76c0","gasPrice":"0x9184e72a000","hash":"0xa2e0da8a8064e0b9f93e95a53c2db6d01280efb8ac72a708d25487e67dd0f8fc","input":"0x","networkId":null,"nonce":"0x1","publicKey":null,"r":"0x1","raw":"0xe9018609184e72a0008276c0940000000000000000000000000000000000000005849184e72a80800101","s":"0x1","standardV":"0x4","to":"0x0000000000000000000000000000000000000005","transactionIndex":null,"v":"0x0","value":"0x9184e72a"},"id":1}"#;
+	let response = r#"{"jsonrpc":"2.0","result":{"blockHash":null,"blockNumber":null,"chainId":null,"condition":null,"creates":null,"from":"0x0000000000000000000000000000000000000002","gas":"0x76c0","gasPrice":"0x9184e72a000","hash":"0xa2e0da8a8064e0b9f93e95a53c2db6d01280efb8ac72a708d25487e67dd0f8fc","input":"0x","nonce":"0x1","publicKey":null,"r":"0x1","raw":"0xe9018609184e72a0008276c0940000000000000000000000000000000000000005849184e72a80800101","s":"0x1","standardV":"0x4","to":"0x0000000000000000000000000000000000000005","transactionIndex":null,"v":"0x0","value":"0x9184e72a"},"id":1}"#;
 
 	miner.pending_transactions.lock().insert(hash, signed);
 	assert_eq!(io.handle_request_sync(&request), Some(response.to_owned()));
diff --git a/rpc/src/v1/tests/mocked/signer.rs b/rpc/src/v1/tests/mocked/signer.rs
index f92486d16..6827334de 100644
--- a/rpc/src/v1/tests/mocked/signer.rs
+++ b/rpc/src/v1/tests/mocked/signer.rs
@@ -454,12 +454,13 @@ fn should_confirm_sign_transaction_with_rlp() {
 	let response = r#"{"jsonrpc":"2.0","result":{"#.to_owned() +
 		r#""raw":"0x"# + &rlp.to_hex() + r#"","# +
 		r#""tx":{"# +
-		r#""blockHash":null,"blockNumber":null,"condition":null,"creates":null,"# +
+		r#""blockHash":null,"blockNumber":null,"# +
+		&format!("\"chainId\":{},", t.chain_id().map_or("null".to_owned(), |n| format!("{}", n))) +
+		r#""condition":null,"creates":null,"# +
 		&format!("\"from\":\"0x{:?}\",", &address) +
 		r#""gas":"0x989680","gasPrice":"0x1000","# +
 		&format!("\"hash\":\"0x{:?}\",", t.hash()) +
 		r#""input":"0x","# +
-		&format!("\"networkId\":{},", t.network_id().map_or("null".to_owned(), |n| format!("{}", n))) +
 		r#""nonce":"0x0","# +
 		&format!("\"publicKey\":\"0x{:?}\",", t.public_key().unwrap()) +
 		&format!("\"r\":\"0x{}\",", U256::from(signature.r()).to_hex()) +
diff --git a/rpc/src/v1/tests/mocked/signing.rs b/rpc/src/v1/tests/mocked/signing.rs
index 91d792253..4c6951f1a 100644
--- a/rpc/src/v1/tests/mocked/signing.rs
+++ b/rpc/src/v1/tests/mocked/signing.rs
@@ -297,12 +297,13 @@ fn should_add_sign_transaction_to_the_queue() {
 	let response = r#"{"jsonrpc":"2.0","result":{"#.to_owned() +
 		r#""raw":"0x"# + &rlp.to_hex() + r#"","# +
 		r#""tx":{"# +
-		r#""blockHash":null,"blockNumber":null,"condition":null,"creates":null,"# +
+		r#""blockHash":null,"blockNumber":null,"# +
+		&format!("\"chainId\":{},", t.chain_id().map_or("null".to_owned(), |n| format!("{}", n))) +
+		r#""condition":null,"creates":null,"# +
 		&format!("\"from\":\"0x{:?}\",", &address) +
 		r#""gas":"0x76c0","gasPrice":"0x9184e72a000","# +
 		&format!("\"hash\":\"0x{:?}\",", t.hash()) +
 		r#""input":"0x","# +
-		&format!("\"networkId\":{},", t.network_id().map_or("null".to_owned(), |n| format!("{}", n))) +
 		r#""nonce":"0x1","# +
 		&format!("\"publicKey\":\"0x{:?}\",", t.public_key().unwrap()) +
 		&format!("\"r\":\"0x{}\",", U256::from(signature.r()).to_hex()) +
diff --git a/rpc/src/v1/types/block.rs b/rpc/src/v1/types/block.rs
index 5a56f962d..10f7a2476 100644
--- a/rpc/src/v1/types/block.rs
+++ b/rpc/src/v1/types/block.rs
@@ -230,7 +230,7 @@ mod tests {
 	fn test_serialize_block_transactions() {
 		let t = BlockTransactions::Full(vec![Transaction::default()]);
 		let serialized = serde_json::to_string(&t).unwrap();
-		assert_eq!(serialized, r#"[{"hash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0","blockHash":null,"blockNumber":null,"transactionIndex":null,"from":"0x0000000000000000000000000000000000000000","to":null,"value":"0x0","gasPrice":"0x0","gas":"0x0","input":"0x","creates":null,"raw":"0x","publicKey":null,"networkId":null,"standardV":"0x0","v":"0x0","r":"0x0","s":"0x0","condition":null}]"#);
+		assert_eq!(serialized, r#"[{"hash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0","blockHash":null,"blockNumber":null,"transactionIndex":null,"from":"0x0000000000000000000000000000000000000000","to":null,"value":"0x0","gasPrice":"0x0","gas":"0x0","input":"0x","creates":null,"raw":"0x","publicKey":null,"chainId":null,"standardV":"0x0","v":"0x0","r":"0x0","s":"0x0","condition":null}]"#);
 
 		let t = BlockTransactions::Hashes(vec![H256::default().into()]);
 		let serialized = serde_json::to_string(&t).unwrap();
diff --git a/rpc/src/v1/types/transaction.rs b/rpc/src/v1/types/transaction.rs
index ee0203d65..d5eb63b44 100644
--- a/rpc/src/v1/types/transaction.rs
+++ b/rpc/src/v1/types/transaction.rs
@@ -59,8 +59,8 @@ pub struct Transaction {
 	#[serde(rename="publicKey")]
 	pub public_key: Option<H512>,
 	/// The network id of the transaction, if any.
-	#[serde(rename="networkId")]
-	pub network_id: Option<u64>,
+	#[serde(rename="chainId")]
+	pub chain_id: Option<u64>,
 	/// The standardised V field of the signature (0 or 1).
 	#[serde(rename="standardV")]
 	pub standard_v: U256,
@@ -196,7 +196,7 @@ impl Transaction {
 			},
 			raw: ::rlp::encode(&t.signed).into_vec().into(),
 			public_key: t.recover_public().ok().map(Into::into),
-			network_id: t.network_id(),
+			chain_id: t.chain_id(),
 			standard_v: t.standard_v().into(),
 			v: t.original_v().into(),
 			r: signature.r().into(),
@@ -230,7 +230,7 @@ impl Transaction {
 			},
 			raw: ::rlp::encode(&t).into_vec().into(),
 			public_key: t.public_key().map(Into::into),
-			network_id: t.network_id(),
+			chain_id: t.chain_id(),
 			standard_v: t.standard_v().into(),
 			v: t.original_v().into(),
 			r: signature.r().into(),
@@ -273,7 +273,7 @@ mod tests {
 	fn test_transaction_serialize() {
 		let t = Transaction::default();
 		let serialized = serde_json::to_string(&t).unwrap();
-		assert_eq!(serialized, r#"{"hash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0","blockHash":null,"blockNumber":null,"transactionIndex":null,"from":"0x0000000000000000000000000000000000000000","to":null,"value":"0x0","gasPrice":"0x0","gas":"0x0","input":"0x","creates":null,"raw":"0x","publicKey":null,"networkId":null,"standardV":"0x0","v":"0x0","r":"0x0","s":"0x0","condition":null}"#);
+		assert_eq!(serialized, r#"{"hash":"0x0000000000000000000000000000000000000000000000000000000000000000","nonce":"0x0","blockHash":null,"blockNumber":null,"transactionIndex":null,"from":"0x0000000000000000000000000000000000000000","to":null,"value":"0x0","gasPrice":"0x0","gas":"0x0","input":"0x","creates":null,"raw":"0x","publicKey":null,"chainId":null,"standardV":"0x0","v":"0x0","r":"0x0","s":"0x0","condition":null}"#);
 	}
 
 	#[test]
diff --git a/sync/src/tests/consensus.rs b/sync/src/tests/consensus.rs
index 499b7de17..9b01156b7 100644
--- a/sync/src/tests/consensus.rs
+++ b/sync/src/tests/consensus.rs
@@ -42,7 +42,7 @@ impl IoHandler<ClientIoMessage> for TestIoHandler {
 	}
 }
 
-fn new_tx(secret: &Secret, nonce: U256, network_id: u64) -> PendingTransaction {
+fn new_tx(secret: &Secret, nonce: U256, chain_id: u64) -> PendingTransaction {
 	let signed = Transaction {
 		nonce: nonce.into(),
 		gas_price: 0.into(),
@@ -50,7 +50,7 @@ fn new_tx(secret: &Secret, nonce: U256, network_id: u64) -> PendingTransaction {
 		action: Action::Call(Address::default()),
 		value: 0.into(),
 		data: Vec::new(),
-	}.sign(secret, Some(network_id));
+	}.sign(secret, Some(chain_id));
 	PendingTransaction::new(signed, None)
 }
 
@@ -62,7 +62,7 @@ fn authority_round() {
 	ap.insert_account(s0.secret().clone(), "").unwrap();
 	ap.insert_account(s1.secret().clone(), "").unwrap();
 
-	let network_id = Spec::new_test_round().network_id();
+	let chain_id = Spec::new_test_round().chain_id();
 	let mut net = TestNet::with_spec_and_accounts(2, SyncConfig::default(), Spec::new_test_round, Some(ap));
 	let io_handler0: Arc<IoHandler<ClientIoMessage>> = Arc::new(TestIoHandler { client: net.peer(0).chain.clone() });
 	let io_handler1: Arc<IoHandler<ClientIoMessage>> = Arc::new(TestIoHandler { client: net.peer(1).chain.clone() });
@@ -76,15 +76,15 @@ fn authority_round() {
 	// exchange statuses
 	net.sync();
 	// Trigger block proposal
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 0.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 0.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 0.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 0.into(), chain_id)).unwrap();
 	// Sync a block
 	net.sync();
 	assert_eq!(net.peer(0).chain.chain_info().best_block_number, 1);
 	assert_eq!(net.peer(1).chain.chain_info().best_block_number, 1);
 
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 1.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 1.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 1.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 1.into(), chain_id)).unwrap();
 	// Move to next proposer step.
 	net.peer(0).chain.engine().step();
 	net.peer(1).chain.engine().step();
@@ -93,8 +93,8 @@ fn authority_round() {
 	assert_eq!(net.peer(1).chain.chain_info().best_block_number, 2);
 
 	// Fork the network with equal height.
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 2.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 2.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 2.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 2.into(), chain_id)).unwrap();
 	// Let both nodes build one block.
 	net.peer(0).chain.engine().step();
 	let early_hash = net.peer(0).chain.chain_info().best_block_hash;
@@ -116,8 +116,8 @@ fn authority_round() {
 	assert_eq!(ci1.best_block_hash, early_hash);
 
 	// Selfish miner
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 3.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 3.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 3.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 3.into(), chain_id)).unwrap();
 	// Node 0 is an earlier primary.
 	net.peer(0).chain.engine().step();
 	assert_eq!(net.peer(0).chain.chain_info().best_block_number, 4);
@@ -128,7 +128,7 @@ fn authority_round() {
 	// Node 1 makes 2 blocks, but is a later primary on the first one.
 	net.peer(1).chain.engine().step();
 	net.peer(1).chain.engine().step();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 4.into(), network_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 4.into(), chain_id)).unwrap();
 	net.peer(1).chain.engine().step();
 	net.peer(1).chain.engine().step();
 	assert_eq!(net.peer(1).chain.chain_info().best_block_number, 5);
@@ -149,7 +149,7 @@ fn tendermint() {
 	ap.insert_account(s0.secret().clone(), "").unwrap();
 	ap.insert_account(s1.secret().clone(), "").unwrap();
 
-	let network_id = Spec::new_test_tendermint().network_id();
+	let chain_id = Spec::new_test_tendermint().chain_id();
 	let mut net = TestNet::with_spec_and_accounts(2, SyncConfig::default(), Spec::new_test_tendermint, Some(ap));
 	let io_handler0: Arc<IoHandler<ClientIoMessage>> = Arc::new(TestIoHandler { client: net.peer(0).chain.clone() });
 	let io_handler1: Arc<IoHandler<ClientIoMessage>> = Arc::new(TestIoHandler { client: net.peer(1).chain.clone() });
@@ -165,7 +165,7 @@ fn tendermint() {
 	// Exhange statuses
 	net.sync();
 	// Propose
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 0.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 0.into(), chain_id)).unwrap();
 	net.sync();
 	// Propose timeout, synchronous for now
 	net.peer(0).chain.engine().step();
@@ -176,7 +176,7 @@ fn tendermint() {
 	assert_eq!(net.peer(0).chain.chain_info().best_block_number, 1);
 	assert_eq!(net.peer(1).chain.chain_info().best_block_number, 1);
 
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 0.into(), network_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 0.into(), chain_id)).unwrap();
 	// Commit timeout
 	net.peer(0).chain.engine().step();
 	net.peer(1).chain.engine().step();
@@ -190,8 +190,8 @@ fn tendermint() {
 	assert_eq!(net.peer(0).chain.chain_info().best_block_number, 2);
 	assert_eq!(net.peer(1).chain.chain_info().best_block_number, 2);
 
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 1.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 1.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 1.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 1.into(), chain_id)).unwrap();
 	// Peers get disconnected.
 	// Commit
 	net.peer(0).chain.engine().step();
@@ -199,8 +199,8 @@ fn tendermint() {
 	// Propose
 	net.peer(0).chain.engine().step();
 	net.peer(1).chain.engine().step();
-	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 2.into(), network_id)).unwrap();
-	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 2.into(), network_id)).unwrap();
+	net.peer(0).chain.miner().import_own_transaction(&*net.peer(0).chain, new_tx(s0.secret(), 2.into(), chain_id)).unwrap();
+	net.peer(1).chain.miner().import_own_transaction(&*net.peer(1).chain, new_tx(s1.secret(), 2.into(), chain_id)).unwrap();
 	// Send different prevotes
 	net.sync();
 	// Prevote timeout