From the Wikipedia page [https://en.wikipedia.org/wiki/Bailiwick_of_Guernsey
The Bailiwick of Guernsey (French: Bailliage de Guernesey) is one of three Crown dependencies.
Separated from the Dukedom and Duchy of Normandy by and under the terms of the Treaty (or Peace) of Le Goulet in 1204, the Bailiwick comprises a number of islands in the English Channel which fall into three separate sub-jurisdictions: Guernsey, Alderney and Sark.
A bailiwick is a territory administered by a Bailiff. The Bailiff of Guernsey is the civil head, and presiding officer of the States of Guernsey, but not of Alderney or Sark. He is the head of the judiciary of the Bailiwick.
The Bailiwick of Guernsey is a separate jurisdiction in itself, and is in turn also three separate sub-jurisdictions. It does not form part of, and is separate from (but is not independent of, or from) the United Kingdom.
The two Bailiwicks of Jersey and Guernsey together make up the Channel Islands.
The Islanders have never had formal representation in the House of Commons of the British Parliament, nor in the European Parliament. Those Islanders, who were not somehow qualified and eligible in their own right to register to vote and to vote in the United Kingdom under the Representation of the People Acts as overseas voters, were excluded from the 2016 United Kingdom European Union membership referendum.
A unique constitutional position has arisen as successive British monarchs have confirmed the liberties and privileges of the Bailiwick, often referring to the so-called Constitutions of King John, a legendary document supposed to have been granted by King John in the aftermath of 1204. Governments of the Bailiwick have generally tried to avoid testing the limits of the unwritten constitution by avoiding conflict with British governments.
The Bailiwick comprises twelve Parishes, Alderney, Sark and ten on Guernsey. Each parish has a parish church from the 11th century, with strong religious control exercised initially from the French Catholic church and for the last 500 years from the English church. Over the years the religious aspect of the administration of each Parish has been reduced in favour of democratically elected Douzeniers.