The term British Islands is used in the law of the United Kingdom to refer collectively to the following four states:

• the United Kingdom of Great Britain and Northern Ireland;
• the Bailiwick of Jersey;
• the Bailiwick of Guernsey (including Alderney, Herm, and Sark); and
• the Isle of Man.

The latter three territories are Crown dependencies and are not a part of the United Kingdom. The Parliament of the United Kingdom on occasions introduces legislation that is extended to the islands, normally by the use of Orders in Council. For this reason it has been found useful to have a collective term for the combined territories. Dating back to 1889, the current formal definition can be found in the Interpretation Act 1978, an Act of the Parliament of the United Kingdom: