The siege of Warsaw in 1939 was fought between the Polish Warsaw Army (Polish: Armia Warszawa) garrisoned and entrenched in Warsaw and the invading German Army.: 70–78 It began with huge aerial bombardments initiated by the Luftwaffe starting on September 1, 1939 following the Nazi invasion of Poland. Land fighting started on September 8, when the first German armored units reached the Wola district and south-western suburbs of the city. Despite German radio broadcasts claiming to have captured Warsaw, the initial enemy attack was repelled and soon afterwards Warsaw was placed under siege. The siege lasted until September 28, when the Polish garrison, commanded under General Walerian Czuma, officially capitulated. The following day approximately 140,000 Polish troops left the city and were taken as prisoners of war. On October 1 the Wehrmacht entered Warsaw, which started a period of German occupation that lasted until the devastating Warsaw Uprising and later until January 17, 1945, when the Wehrmacht troops abandoned the city due to the advance of Soviet forces.

Around 18,000 civilians of Warsaw perished during the siege. As a result of the air bombardments, 10% of the city's buildings were entirely destroyed and further 40% were heavily damaged.: 78 Under the international rules regarding aerial warfare in 1939 Warsaw was considered a legitimate military target as the city was on the front line during the fighting and it was heavily defended by the Polish army.