This is a list of referendums related to the European Union, or referendums related to the European Communities, which were predecessors of the European Union. Since 1972, a total of 48 referendums have been held by EU member states, candidate states, and their territories, with several additional referendums held in countries outside of the EU. The referendums have been held most commonly on the subject of whether to become a member of European Union as part of the accession process, although the EU does not require any candidate country to hold a referendum to approve membership or as part of treaty ratification. Other EU-related referendums have been held on the adoption of the euro and on participation in other EU-related policies.