An independence referendum was held in Montenegro on 21 May 2006. It was approved by 55.5% of voters, narrowly passing the 55% threshold. By 23 May, preliminary referendum results were recognized by all five permanent members of the United Nations Security Council, suggesting widespread international recognition if Montenegro were to become formally independent. On 31 May, the referendum commission officially confirmed the results of the referendum, verifying that 55.5% of the population of Montenegrin voters had voted in favor of independence. Because voters met the controversial threshold requirement of 55% approval, the referendum was incorporated into a declaration of independence during a special parliamentary session on 31 May. The Assembly of the Republic of Montenegro made a formal Declaration of Independence on Saturday 3 June.In response to the announcement, the government of Serbia declared itself the legal and political successor of Serbia and Montenegro, and that the government and parliament of Serbia itself would soon adopt a new constitution. The United States, China, Russia, and the institutions of the European Union all expressed their intentions to respect the referendum's results.

The Republic of Montenegro (Serbian: Република Црна Гора, romanized: Republika Crna Gora) was a constituent federated state of the Federal Republic of Yugoslavia and then Serbia and Montenegro between 1992 and 2006. The declaration of independence of Montenegro in 2006 ended the ex-Yugoslav state. After the collapse of the Socialist Federal Republic of Yugoslavia (SFRY), the remaining republics of Montenegro and Serbia agreed to the formation of the Federal Republic of Yugoslavia (FRY) which officially abandoned communism and nominally endorsed democratic institutions. Montenegro was a constituent republic of the FRY and its successor state until 2006 when Montenegro declared independence from Serbia and Montenegro following the 2006 Montenegrin independence referendum.