diff --git a/src/client.rs b/src/client.rs
index f67eb0905..9b5d2f26e 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -1,10 +1,11 @@
+use std::sync::Arc;
 use std::path::Path;
 use util::uint::U256;
 use util::hash::*;
-use util::sha3::*;
 use util::rlp::*;
 use util::bytes::Bytes;
 use blockchain::BlockChain;
+use queue::BlockQueue;
 use views::BlockView;
 
 /// Status for a block in a queue.
@@ -106,7 +107,7 @@ pub trait BlockChainClient : Sync {
 	/// Get block queue information.
 	fn queue_status(&self) -> BlockQueueStatus;
 
-	/// Clear block qeueu and abort all import activity.
+	/// Clear block queue and abort all import activity.
 	fn clear_queue(&mut self);
 
 	/// Get blockchain information.
@@ -115,13 +116,16 @@ pub trait BlockChainClient : Sync {
 
 /// Blockchain database client backed by a persistent database. Owns and manages a blockchain and a block queue.
 pub struct Client {
-	chain: BlockChain
+	chain: Arc<BlockChain>,
+	queue: BlockQueue,
 }
 
 impl Client {
 	pub fn new(genesis: &[u8], path: &Path) -> Client {
+		let chain = Arc::new(BlockChain::new(genesis, path));
 		Client {
-			chain: BlockChain::new(genesis, path)
+			chain: chain.clone(),
+			queue: BlockQueue::new(chain)
 		}
 	}
 }
@@ -181,17 +185,7 @@ impl BlockChainClient for Client {
 	}
 
 	fn import_block(&mut self, bytes: &[u8]) -> ImportResult {
-		//TODO: verify block
-		{
-			let block = BlockView::new(bytes);
-			let header = block.header_view();
-			let hash = header.sha3();
-			if self.chain.is_known(&hash) {
-				return ImportResult::Bad;
-			}
-		}
-		self.chain.insert_block(bytes);
-		ImportResult::Queued(QueueStatus::Known)
+		self.queue.import_block(bytes)
 	}
 
 	fn queue_status(&self) -> BlockQueueStatus {
@@ -201,6 +195,7 @@ impl BlockChainClient for Client {
 	}
 
 	fn clear_queue(&mut self) {
+		self.queue.clear();
 	}
 
 	fn chain_info(&self) -> BlockChainInfo {
diff --git a/src/lib.rs b/src/lib.rs
index 1d351444c..80f9b732e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -105,6 +105,7 @@ pub mod views;
 pub mod blockchain;
 pub mod extras;
 pub mod client;
-
 pub mod sync;
+pub mod verification;
+pub mod queue;
 
diff --git a/src/queue.rs b/src/queue.rs
new file mode 100644
index 000000000..8d427e8a1
--- /dev/null
+++ b/src/queue.rs
@@ -0,0 +1,37 @@
+use std::sync::Arc;
+//use util::bytes::*;
+use util::sha3::*;
+use blockchain::BlockChain;
+use client::{QueueStatus, ImportResult};
+use views::{BlockView};
+
+
+pub struct BlockQueue {
+	chain: Arc<BlockChain>
+}
+
+impl BlockQueue {
+	pub fn new(chain: Arc<BlockChain>) -> BlockQueue {
+		BlockQueue {
+			chain: chain
+		}
+	}
+
+	pub fn clear(&mut self) {
+	}
+
+	pub fn import_block(&mut self, bytes: &[u8]) -> ImportResult {
+		//TODO: verify block
+		{
+			let block = BlockView::new(bytes);
+			let header = block.header_view();
+			let hash = header.sha3();
+			if self.chain.is_known(&hash) {
+				return ImportResult::Bad;
+			}
+		}
+		self.chain.insert_block(bytes);
+		ImportResult::Queued(QueueStatus::Known)
+	}
+}
+
diff --git a/src/verification.rs b/src/verification.rs
new file mode 100644
index 000000000..95951da53
--- /dev/null
+++ b/src/verification.rs
@@ -0,0 +1,109 @@
+use util::uint::*;
+use util::hash::*;
+use util::rlp::*;
+use util::sha3::Hashable;
+use util::triehash::ordered_trie_root;
+use header::Header;
+use client::BlockNumber;
+
+#[derive(Debug)]
+pub enum TransactionVerificationError {
+	OutOfGasBase,
+	OutOfGasIntrinsic,
+	NotEnoughCash,
+	GasPriceTooLow,
+	BlockGasLimitReached,
+	FeeTooSmall,
+	TooMuchGasUsed {
+		used: U256,
+		limit: U256
+	},
+	ExtraDataTooBig,
+	InvalidSignature,
+	InvalidTransactionFormat,
+}
+
+#[derive(Debug)]
+pub enum BlockVerificationError {
+	TooMuchGasUsed {
+		used: U256,
+		limit: U256,
+	},
+	InvalidBlockFormat,
+	InvalidUnclesHash {
+		expected: H256,
+		got: H256,
+	},
+	TooManyUncles,
+	UncleTooOld,
+	UncleIsBrother,
+	UncleInChain,
+	UncleParentNotInChain,
+	InvalidStateRoot,
+	InvalidGasUsed,
+	InvalidTransactionsRoot {
+		expected: H256,
+		got: H256,
+	},
+	InvalidDifficulty,
+	InvalidGasLimit,
+	InvalidReceiptsStateRoot,
+	InvalidTimestamp,
+	InvalidLogBloom,
+	InvalidNonce,
+	InvalidBlockHeaderItemCount,
+	InvalidBlockNonce,
+	InvalidParentHash,
+	InvalidUncleParentHash,
+	InvalidNumber,
+	BlockNotFound,
+	UnknownParent,
+}
+
+
+pub fn verify_header(header: &Header) -> Result<(), BlockVerificationError> {
+	if header.number > From::from(BlockNumber::max_value()) {
+		return Err(BlockVerificationError::InvalidNumber)
+	}
+	if header.gas_used > header.gas_limit {
+		return Err(BlockVerificationError::TooMuchGasUsed {
+			used: header.gas_used,
+			limit: header.gas_limit,
+		});
+	}
+	Ok(())
+}
+
+pub fn verify_parent(header: &Header, parent: &Header) -> Result<(), BlockVerificationError> {
+	if !header.parent_hash.is_zero() && parent.hash() != header.parent_hash {
+		return Err(BlockVerificationError::InvalidParentHash)
+	}
+	if header.timestamp <= parent.timestamp {
+		return Err(BlockVerificationError::InvalidTimestamp)
+	}
+	if header.number <= parent.number {
+		return Err(BlockVerificationError::InvalidNumber)
+	}
+	Ok(())
+}
+
+pub fn verify_block_integrity(block: &[u8], transactions_root: &H256, uncles_hash: &H256) -> Result<(), BlockVerificationError> {
+	let block = Rlp::new(block);
+	let tx = block.at(1);
+	let expected_root = ordered_trie_root(tx.iter().map(|r| r.as_raw().to_vec()).collect()); //TODO: get rid of vectors here
+	if &expected_root != transactions_root {
+		return Err(BlockVerificationError::InvalidTransactionsRoot {
+			expected: expected_root.clone(),
+			got: transactions_root.clone(),
+		});
+	}
+	let expected_uncles = block.at(2).as_raw().sha3();
+	if &expected_uncles != uncles_hash {
+		return Err(BlockVerificationError::InvalidUnclesHash {
+			expected: expected_uncles.clone(),
+			got: uncles_hash.clone(),
+		});
+	}
+	Ok(())
+}
+