diff --git a/README.md b/README.md
index 6def7fe..6250bfe 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,27 @@ in CIC native interfaces.
 
 ## Native interfaces
 
+### ACL
+
+A simple Access Control List definition that returns true of false
+depending on whether an signatory (address) is allowed to operate in a
+given context.
+
+#### ERC165 Interface identifier
+
+3ef25013
+
+#### Solidity interface definition
+
+    interface IACL {
+        // Returns true if the address has permission to operate in the given context.
+        function have(address _address) external view returns(bool);
+    }
+
+#### Example implementation
+
+<git://holbrook.no/eth-accounts-index.git>
+
 ### Accounts Index
 
 Append-only list of addresses. Typically used for access control lists.
@@ -83,6 +104,7 @@ b7bca625
         function add(address) external returns (bool);
 
         // Verify that the entry exists in the index.
+        // Implements ACL
         function have(address) external view returns (bool);
 
         // Retrieve the timestamp when account was added.
diff --git a/doc/texinfo/acl.sol.texi b/doc/texinfo/acl.sol.texi
new file mode 100644
index 0000000..1811f3c
--- /dev/null
+++ b/doc/texinfo/acl.sol.texi
@@ -0,0 +1,17 @@
+@subsection ACL
+
+A simple Access Control List definition that returns true of false depending on whether an signatory (address) is allowed to operate in a given context.
+
+@subsubsection ERC165 Interface identifier
+
+@include ../../build/ACL.interface
+
+@subsubsection Solidity interface definition
+
+@include ../../build/contract_ACL.texi
+
+@subsubsection Example implementation
+
+@uref{git://holbrook.no/eth-accounts-index.git,}
+
+
diff --git a/doc/texinfo/overview.texi b/doc/texinfo/overview.texi
index 8751c43..9f6b9c5 100644
--- a/doc/texinfo/overview.texi
+++ b/doc/texinfo/overview.texi
@@ -50,6 +50,8 @@ The following well-known solidity interfaces are partially implemented in CIC na
 
 @section Native interfaces
 
+@include acl.sol.texi
+
 @include accountsindex.sol.texi
 
 @include burner.sol.texi
diff --git a/python/README.md b/python/README.md
index 6def7fe..6250bfe 100644
--- a/python/README.md
+++ b/python/README.md
@@ -47,6 +47,27 @@ in CIC native interfaces.
 
 ## Native interfaces
 
+### ACL
+
+A simple Access Control List definition that returns true of false
+depending on whether an signatory (address) is allowed to operate in a
+given context.
+
+#### ERC165 Interface identifier
+
+3ef25013
+
+#### Solidity interface definition
+
+    interface IACL {
+        // Returns true if the address has permission to operate in the given context.
+        function have(address _address) external view returns(bool);
+    }
+
+#### Example implementation
+
+<git://holbrook.no/eth-accounts-index.git>
+
 ### Accounts Index
 
 Append-only list of addresses. Typically used for access control lists.
@@ -83,6 +104,7 @@ b7bca625
         function add(address) external returns (bool);
 
         // Verify that the entry exists in the index.
+        // Implements ACL
         function have(address) external view returns (bool);
 
         // Retrieve the timestamp when account was added.
diff --git a/solidity/ACL.sol b/solidity/ACL.sol
new file mode 100644
index 0000000..a2c3b5d
--- /dev/null
+++ b/solidity/ACL.sol
@@ -0,0 +1,10 @@
+pragma solidity >=0.6.12;
+
+// Author:	Louis Holbrook <dev@holbrook.no> 0826EDA1702D1E87C6E2875121D2E7BB88C2A746
+// SPDX-License-Identifier:	AGPL-3.0-or-later
+// File-version: 1
+
+interface IACL {
+	// Returns true if the address has permission to operate in the given context.
+	function have(address _address) external view returns(bool);
+}
diff --git a/solidity/AccountsIndex.sol b/solidity/AccountsIndex.sol
index ee9dd0f..60719a0 100644
--- a/solidity/AccountsIndex.sol
+++ b/solidity/AccountsIndex.sol
@@ -20,6 +20,7 @@ interface IAccountsIndex {
 	function add(address) external returns (bool);
 
 	// Verify that the entry exists in the index.
+	// Implements ACL
 	function have(address) external view returns (bool);
 
 	// Retrieve the timestamp when account was added.