The history of Poland from 1939 to 1945 encompasses primarily the period from the invasion of Poland by Nazi Germany and the Soviet Union to the end of World War II. Following the German–Soviet non-aggression pact, Poland was invaded by Nazi Germany on 1 September 1939 and by the Soviet Union on 17 September. The campaigns ended in early October with Germany and the Soviet Union dividing and annexing the whole of Poland. After the Axis attack on the Soviet Union in the summer of 1941, the entirety of Poland was occupied by Germany, which proceeded to advance its racial and genocidal policies across Poland.

Poland, officially the Republic of Poland, is a country in Central Europe. It extends from the Baltic Sea in the north to the Sudetes and Carpathian Mountains in the south, while its longest river is the Vistula. Poland has a temperate transitional climate and is the fifth-most populous member state of the European Union, with its sixteen voivodeships having a total population of over 38 million and covering a combined area of 312,696 km2 (120,733 sq mi). It is bordered by Lithuania and Russia to the northeast, Belarus and Ukraine to the east, Slovakia and the Czech Republic to the south, and Germany to the west. The nation's capital and largest metropolis is Warsaw. Other major cities include Kraków, Wrocław, Łódź, Poznań, and Gdańsk.