Crown dependencies are possessions of the British Crown, as opposed to overseas territories or colonies of the United Kingdom. They comprise the Channel Island bailiwicks of Jersey and Guernsey and the Isle of Man in the Irish Sea.

None forms part of the United Kingdom, being independently administrated jurisdictions, nor do they form part of the European Union. All three Crown dependencies are members of the British-Irish Council. From 2005, each Crown dependency has a Chief Minister as head of government. However, as they are possessions of the British Crown they are not sovereign nations in their own right, and the power to pass legislation affecting the islands rests ultimately with the British Parliament.

These Crown dependencies, together with the United Kingdom, are collectively known as the British Islands. They are treated as part of the United Kingdom for British nationality law purposes. However they maintain local controls over housing and employment which apply to British citizens without specified connections to that dependency (as well as to non-British citizens).

Each Island has its own separate international vehicle registration (GBG – Guernsey, GBA – Alderney, GBJ – Jersey, GBM – Isle of Man), internet domain (.gg – Guernsey, .je – Jersey, .im – Isle of Man), and ISO 3166-2 codes, first reserved on behalf of the Universal Postal Union (GGY – Guernsey, JEY – Jersey, IMN – Isle of Man) and then added officially by the International Organization for Standardization on March 29, 2006.