Croatia held a referendum in which it voted to become a member of the European Union.

A referendum on the EU accession of the Republic of Croatia was held on 22 January 2012. Croatia finished accession (membership) negotiations on 30 June 2011 and signed the Treaty of Accession on 9 December 2011, setting it on course to become the bloc's 28th member state. The Constitution of Croatia requires that a binding referendum be held on any political union reducing national sovereignty, such as via European Union membership. On 23 December 2011 the Croatian Parliament made a preliminary decision on EU accession and determined that the referendum would be held on 22 January 2012. The 2012 Croatian EU accession referendum was the first referendum held in Croatia since the Croatian independence referendum held more than 20 years earlier, in 1991.

The European Union (EU) is a supranational political and economic union of 27 member states that are located primarily in Europe. The union has a total area of 4,233,255 km² (1,634,469 sq mi) and an estimated population of over 450 million as of 2025. The EU is often described as a sui generis political entity combining characteristics of both a federation and a confederation.