Lebensraum (German pronunciation: [ˈleːbənsˌʁaʊm] (listen), living space) is a German concept of settler colonialism, the philosophy and policies of which were common to German politics from the 1890s to the 1940s. First popularized around 1901, Lebensraum became a geopolitical goal of Imperial Germany in World War I (1914–1918), as the core element of the Septemberprogramm of territorial expansion. The most extreme form of this ideology was supported by the Nazi Party and Nazi Germany. Lebensraum was a leading motivation of Nazi Germany to initiate World War II, and it would continue this policy until the end of World War II.

Following Adolf Hitler's rise to power, Lebensraum became an ideological principle of Nazism and provided justification for the German territorial expansion into Central and Eastern Europe. The Nazi policy Generalplan Ost (lit. 'Master Plan for the East') was based on its tenets. It stipulated that Germany required a Lebensraum necessary for its survival and that most of the indigenous populations of Central and Eastern Europe would have to be removed permanently (either through mass deportation to Siberia, extermination, or enslavement), including Polish, Ukrainian, Russian, Czech, and other Slavic nations considered non-Aryan. The Nazi government aimed at repopulating these lands with Germanic colonists in the name of Lebensraum during and following World War II. Entire indigenous populations were decimated by starvation, allowing for their own agricultural surplus to feed Germany.

Hitler's strategic program for world domination was based on the belief in the power of Lebensraum, especially when pursued by a racially superior society. People deemed to be part of non-Aryan races, within the territory of Lebensraum expansion, were subjected to expulsion or destruction. The eugenics of Lebensraum assumed it to be the right of the German Aryan master race (Herrenvolk) to remove the indigenous people in the name of their own living space. They took inspiration for this concept from outside Germany. Hitler and Nazi officials took a particular interest in manifest destiny, and attempted to replicate it in occupied Europe. Nazi Germany also supported other Axis Powers' expansionist ideologies such as Fascist Italy's spazio vitale and Imperial Japan's Hakkō ichiu.