Southeast Europe or Southeastern Europe is a relatively recent political designation mostly for the states of the Balkans. Writers such as Maria Todorova and Vesna Goldsworthy have suggested the use of the term Southeastern Europe to replace the word Balkans for the region, to minimize potential misunderstandings about the term Balkans having negative connotations.

The first known usage of the term 'Southeast Europe' was by Austrian researcher Johann Georg von Hahn (1811–1869) as broader term than the traditional Balkans. Unlike the United Nations definitions of Eastern Europe, Western Europe, Southern Europe and Northern Europe, there are no clear and universally accepted geographical or historical divisions that delineate this region. However, if United Nations definitions of bordering macroregions are done, the rest can be considered as Central Europe.

There are four possible definitions of "Southeastern Europe". The Balkan Peninsula south of the River Danube-River Sava-River Kupa line; the European territories of the former Ottoman Empire; and the substantially larger space with a northern delineation that respects actual borders, promoted by the European Union from 1999. Finally, there is a European Union co-funded regional development model that adds Austria, the eastern Regions of Italy and southwestern Ukraine.