The 1929 U.S. stock-market day when the Dow Jones Industrial Average fell 12.8% on October 28 was Black Monday.
Black Monday was the first of two devastating sessions late in October 1929. On October 28, the Dow lost 38.33 points, equal to 12.8% of its value at the time. The next day, October 29, brought another huge decline and is widely known as Black Tuesday. Together, the sessions ended the speculative boom of the 1920s.
The crash did not by itself cause every feature of the Great Depression, but it severely damaged confidence and wealth. Bank failures, falling demand, debt problems, deflation, and policy mistakes deepened the economic collapse afterward. Black Monday is often confused with the 1987 crash, which also occurred on a Monday and is also called Black Monday. The dates and economic settings are entirely different.