Montenegrin–Serbian relations are foreign relations between Montenegro and Serbia. From 1918 until 2006 the two states were united under the Kingdom of Yugoslavia, the Socialist Federal Republic of Yugoslavia, and Serbia and Montenegro. There is controversy regarding the national identity of Montenegro due to recent political developments in the region. There is a debate on the ethnic identification of Montenegrins (whether they are Serbs or not), and the name of the national language (Montenegrin versus Serbian). Despite this, the two countries have maintained mostly friendly relations.