The Hallstein Doctrine, named after Walter Hallstein, was a key doctrine in the foreign policy of the Federal Republic of Germany (West Germany) between 1955 and 1969.

According to the doctrine, the Federal Republic of Germany had the exclusive right to represent the entire German nation, and with the exception of the Soviet Union, West Germany would not establish or maintain diplomatic relations with any state that recognized East Germany. The doctrine was first applied to Yugoslavia in 1957, and is directly comparable to the One-China policy of the People's Republic of China.

East Germany attempted to undermine this doctrine by forming diplomatic relationships with the newly decolonized nations of the Third World.

The doctrine was never popular, even with West Germany's western allies, as it effectively tried to impose retroactive conditions on the unconditional surrender of 1945, and it was abandoned with the adoption of Ostpolitik by Chancellor Willy Brandt, which resulted in mutual recognition between East and West Germany as two states (though not as two nations).

Not every divided country applied this doctrine like in Germany. During the Vietnam war for instance, there was not really a Hallstein Doctrine in either North Vietnam or South Vietnam. In fact, at the beginning of the war, a country which had recognized either the North or the South would rarely recognize the other half, for political reasons, but when some European countries started recognizing North Vietnam towards the end of the war, like Switzerland in 1971, South Vietnam did not interrupt its diplomatic relations with them. Switzerland thus recognized North Vietnam in 1971 but also turned its consulate in Saigon (South Vietnam) into an embassy until the end of the war in 1975.