Western betrayal or Yalta betrayal are popular terms in many Central European countries, especially in Poland and the Czech Republic but also in non-Western nations which refers to the foreign policy of several Western countries which violated allied pacts and agreements during the period from the Treaty of Versailles in 1919 through World War II and to the Cold War, as rooted in hypocrisy and betrayal.

The "betrayal" refers to the claim that the western Allies—in spite of having promoted democracy and self-determination, signing pacts and forming military alliances prior and during World War II—nonetheless betrayed their Central European allies by abandoning these pacts. For example by not preventing Nazi Germany from invading and occupying Czechoslovakia or abandoning its Polish ally during 1939 Polish September Campaign and 1944 Warsaw Uprising. After World War II, Western powers did nothing or very little to prevent these states from falling under the influence and control of Soviet communism.

The concept is disputed by those historians who argue that Prime Minister of the United Kingdom Winston Churchill and President of the United States Franklin Roosevelt had no option but to accept the demands of their ally Soviet premier Joseph Stalin in Tehran and later in Yalta. However, there is certainty that there were some misjudgments of the power of the Soviet Union by elements within the Western powers, much like the case with Nazi Germany a decade before. Supporters of Yalta are sometimes outraged at the notion that Yalta was a “betrayal” of Eastern and Central Europe without considering the fate of Poland. Polish forces had fought the Nazis longer than any country; they fought alongside the U.S. and British in every major campaign in Europe and made up the fourth largest army in the fight against Hitler; the Polish government in exile was an official ally of the U.S. and Britain. This did not prevent Roosevelt from acquiescing in the dismantlement of this Allied government and its replacement with a "puppet" communist government. Even as the men of the Polish 1st Armoured Division, determined to link up with the American 90th Division under Gen. George S. Patton and to close the trap on Nazi armies in Normandy, were battling the Germans and SS Hitlerjugend divisions, Roosevelt was planning to hand Poland over to Stalin.

Other historians suggest that Churchill urged Roosevelt to continue military action in Europe but against the Soviet Union to prevent the USSR extending its control beyond its own borders. Roosevelt apparently trusted Stalin's assurances and declined to support Churchill's intention of ensuring the liberty of all Europe outside the USSR. Without US backing, the exhausted, near bankrupt, and close to starving UK could not take action. Even with US backing, the result of action against the Soviet Union was uncertain (see Operation Unthinkable).