The occupation of Greece by the Axis Powers (Greek: , romanized: I Katochi, lit.'the occupation') began in April 1941 after Nazi Germany invaded the Kingdom of Greece to assist its ally, Fascist Italy, which had been at war with Allied Greece since October 1940. Following the conquest of Crete, all of Greece was occupied by June 1941. The occupation of the mainland lasted until Germany and its ally Bulgaria were forced to withdraw under Allied pressure in early October 1944. However, German garrisons remained in control of Crete and some other Aegean islands until after the end of World War II in Europe, surrendering these islands in May and June 1945.

Fascist Italy had initially declared war and invaded Greece in October 1940, but the Hellenic Army managed to push back the invading forces into neighboring Albania, then an Italian protectorate. Nazi Germany intervened on its ally's behalf in southern Europe. While most of the Hellenic Army was dislocated on the Albanian front to fend off the relentless Italian counter-attacks, a rapid German Blitzkrieg campaign commenced in April 1941, and by June (with the conquest of Crete) Greece was defeated and occupied. The Greek government went into exile, and an Axis collaborationist puppet government was established in the country. Greece's territory was divided into occupation zones run by the Axis powers, with the Germans administering the most important regions of the country themselves, including Athens, Thessaloniki and the strategic Aegean Islands. Other regions of the country were given to Germany's partners, Italy and Bulgaria.

The occupation ruined the Greek economy and brought terrible hardships to the Greek civilian population. Much of Greece was subjected to destruction of its industry (80% of which was destroyed), infrastructure (28% destroyed), ports, roads, railways and bridges (90%), forests and other natural resources (25%) and loss of civilian life (7.0211.17% of its citizens). Over 40,000 civilians died in Athens alone from starvation, and tens of thousands more died from reprisals by Nazis and collaborators.The Jewish population of Greece was nearly eradicated. Of its pre-war population of 7577,000, only around 1112,000 survived, either by joining the resistance or being hidden. Most of those who died were deported to Auschwitz, while those in Thrace, under Bulgarian occupation, were sent to Treblinka. The Italians did not deport Jews living in territory they controlled, but when the Germans took over, Jews living there were also deported.

At the same time the Greek Resistance was formed. These resistance groups launched guerrilla attacks against the occupying powers, fought against the collaborationist Security Battalions, and set up espionage networks. By late 1943 the resistance groups began to fight amongst themselves. When liberation of the mainland came in October 1944, Greece was in a state of political polarization, which soon led to the outbreak of the Greek Civil War. The subsequent civil war gave the opportunity to many prominent Nazi collaborators not only to escape punishment (because of their anti-communism), but to eventually become the ruling class of postwar Greece, after the communist defeat.The Greek Resistance killed 21,087 Axis soldiers (17,536 Germans, 2,739 Italians, 1,532 Bulgarians) and captured 6,463 (2,102 Germans, 2,109 Italians, 2,252 Bulgarians), for the death of 20,650 Greek partisans and an unknown number captured.

Ioannis Rallis (Greek: Ιωάννης Δ. Ράλλης; 1878 – 26 October 1946) was the third and last collaborationist prime minister of Greece during the Axis occupation of Greece during World War II, holding office from 7 April 1943 to 12 October 1944, succeeding Konstantinos Logothetopoulos in the Nazi-controlled Greek puppet government in Athens.