Ireland and the United Kingdom are the only parts of the European Union not obliged to join the Schengen free-travel area. The Crown Dependencies, which are outside of the EU, are not members either. Instead, a Common Travel Area exists between the two states and the Crown Dependencies. The Common Travel Areas is not founded on any formal agreement between Ireland and the United Kingdom and is not provided for in legislation. Instead, it is an informal arrangement between the states. When the Schengen Area was incorporated into the European Union through the 1992 Amsterdam Treaty, the first formal recognition of the Common Travel areas was made though an annexed protocol exempting their obligations to join.