The BES islands (i.e., Bonaire, Saba, and Sint Eustatius) became direct parts of the Netherlands, which is itself the major constituent country of the Kingdom. As special municipalities, they were constituted as "public bodies" () under the Constitution for the Kingdom of the Netherlands. These municipalities resemble ordinary Dutch municipalities in most ways (e.g., they have mayors, aldermen, and municipal councils) and the laws of the Netherlands would operate in them. As a transitional measure, however, only Netherlands law necessary to function within its legal system took immediate effect when the BES islands joined the Netherlands on 10 October 2010, while most laws of the Netherlands Antilles remained in force. Since that date, Dutch legislation slowly replaced Netherlands Antilles laws. Nevertheless, some derogations exist: e.g., social security is not at the same level as in the European part of the Netherlands, and the islands' currency is the U.S. dollar, not the euro.