The 1977 Vrancea earthquake occurred on 4 March 1977, at 21:22 local time, and was felt throughout the Balkans. It had a magnitude of 7.5, making it the second most powerful earthquake recorded in Romania in the 20th century, after the 10 November 1940 seismic event. The hypocenter was situated in the Vrancea Mountains, the most seismically active part of Romania, at a depth of 85.3 km.The earthquake killed about 1,578 people (1,424 in Bucharest) in Romania, and wounded more than 11,300. Among the victims were actor Toma Caragiu and writers A. E. Bakonsky, Alexandru Ivasiuc and Corneliu M. Popescu. Communist ruler Nicolae Ceaușescu suspended his official visit to Nigeria and declared a state of emergency.

About 32,900 buildings were damaged or destroyed. Immediately after the earthquake, 35,000 families were without shelter. The economic losses are believed to have been as high as two billion US dollars though the sum was not confirmed by the authorities at that time. A detailed report on the destruction the earthquake caused was never published. Most of the damage was concentrated in Romania's capital, Bucharest, where about 33 large buildings collapsed. Most of those buildings were built before World War II, and were not reinforced. After the earthquake, the Romanian government imposed tougher construction standards, and would use the earthquake as a pretext to start the major demolitions campaign in Bucharest in 1982, a campaign that lasted up to 1991.

In Bulgaria the earthquake is known as the Vrancea earthquake or Svishtov earthquake. Three blocks of flats in the Bulgarian town of Svishtov (near Zimnicea) collapsed, killing more than 100 people. Many other buildings were damaged, including the Church of the Holy Trinity. In Soviet Moldavia the earthquake destroyed and damaged many buildings; in the capital Chișinău a panic broke out.