The Iran hostage crisis (Persian: تصرف سفارت آمریکا ) was a diplomatic crisis between Iran and the United States where 52 U.S. diplomats were held hostage for 444 days from November 4, 1979 to January 20, 1981, after a group of Islamist student radicals took over the American embassy in support of the Iranian revolution.

The crisis has been described as an entanglement of "vengeance and mutual incomprehension". In Iran the incident was seen by many as a blow against the U.S., its influence in Iran, its percieved attempts to undermine the Iranian Revolution, and its long standing support of the recently overthrown Shah of Iran, Mohammad Reza Pahlavi. The Shah had been restored to power by a CIA-funded coup in 1953 and had recently been allowed into the United States for cancer treatment. In the United States, the hostage-taking was widely seen as an outrage violating a centuries-old principle of international law granting diplomats immunity from arrest and diplomatic compounds sovereignty in the territory of the host country they occupy.

The ordeal reached a climax when after failed attempts to negotiate a release, the United States military attempted a rescue operation, Operation Eagle Claw, on April 24, 1980, which resulted in an aborted mission, the crash of two aircraft and the deaths of eight American military men. The crisis ended with the signing of the Algiers Accords in Algeria on January 19, 1981. The hostages were formally released into United States custody the following day, just minutes after the new American president Ronald Reagan was sworn in.

In America, the crisis is thought by some political analysts to be the primary reason for U.S. President Jimmy Carter's defeat in the November 1980 presidential election, and described by some as the "pivotal episode" in the history of U.S.-Iranian relations. In Iran, the crisis radicalized the revolution, strengthening the prestige of the Ayatollah Khomeini and the political power of radical anti-American forces who supported the hostage taking. The crisis also marked the beginning of American legal action, or sanctions, that weakened economic ties between Iran and America. Sanctions blocked all property within U.S. jurisdiction owned by the Central Bank and Government of Iran.