The Common Travel Area (CTA; ) is an open borders area comprising the United Kingdom, Ireland, the Isle of Man, and the Channel Islands. The British Overseas Territories are not included. Based on agreements that are not legally binding, the internal borders of the CTA are subject to minimal controls, if any, and can normally be crossed by British and Irish citizens with minimal identity documents with certain exceptions. The maintenance of the CTA involves co-operation on immigration matters between the British and Irish authorities.