During the Second World War, Pope Pius XII maintained links to the German resistance to Nazism against Adolf Hitler's Nazi regime. Although remaining publicly neutral, Pius advised the British in 1940 of the readiness of certain German generals to overthrow Hitler if they could be assured of an honourable peace, offered assistance to the German resistance in the event of a coup, and warned the Allies of the planned German invasion of the Low Countries in 1940. The Nazis considered that the Pope had engaged in acts equivalent to espionage.

Catholic resistance to Nazi Germany was a component of German resistance to Nazism and of Resistance during World War II. The role of the Catholic Church during the Nazi years remains a matter of much contention. From the outset of Nazi rule in 1933, issues emerged which brought the church into conflict with the regime and persecution of the church led Pope Pius XI to denounce the policies of the Nazi Government in the 1937 papal encyclical Mit brennender Sorge. His successor Pius XII faced the war years and provided intelligence to the Allies. Catholics fought on both sides in World War II and neither the Catholic nor Protestant churches as institutions were prepared to openly oppose the Nazi State.