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.