The 1991 Soviet coup d'état attempt, also known as the August Coup, was a failed attempt by hard-liners of the Soviet Union's Communist Party to take control of the country away from Mikhail Gorbachev, who was Soviet President and General Secretary of the Party. The coup leaders consisted of top military and civilian officials, including Vice President Gennady Yanayev, who formed the State Committee on the State of Emergency (GKChP). They were opponents of Gorbachev's reform program, angry at the loss of control over Eastern European states and fearful of the New Union Treaty that was about to be signed. The treaty would decentralize much of the central government's power to the 15 republics.

The GkChP hard-liners dispatched KGB agents, who detained Gorbachev at his holiday estate but failed to detain the recently elected president of a newly reconstituted Russia, Boris Yeltsin, who had been both an ally and critic of Gorbachev. The GKChP was poorly organized, resisted effectively by both Yeltsin and a civilian campaign of anti-Communist protestors, mainly in Moscow. The coup collapsed in only two days and Gorbachev returned to office, while all the plotters lost office. Yeltsin became the dominant leader and Gorbachev lost much of his influence. The failed coup led to both the immediate collapse of the Communist Party of the Soviet Union and the dissolution of the USSR four months later.

Following the capitulation of the GKChP, popularly referred to as the "Gang of Eight", both the Supreme Court of the Russian Soviet Federative Socialist Republic (RSFSR) and the President of the Soviet Union Mikhail Gorbachev described their actions as a coup attempt.