In the 1929 Wall Street Crash, the Dow Jones Industrial Average fell 12.8% on Black Tuesday, October 29, 1929.
Black Tuesday followed Black Thursday, October 24, and Black Monday, October 28. Heavy selling overwhelmed the New York Stock Exchange, and the Dow lost about 30 points, a record decline at the time. The crash became the most famous event in the wider collapse that helped begin the Great Depression.
The crash did not by itself cause every aspect of the Great Depression. Falling investment, bank failures, reduced consumer demand, international debt problems, and policy responses all contributed to the prolonged economic crisis. The Dow had risen dramatically during the 1920s, encouraging speculation and purchases made with borrowed money.
A common mix-up is treating Black Tuesday as the only major crash day. The sequence of late-October 1929 losses was important, and the market continued falling after October 29. The Dow eventually reached a low in July 1932, far below its 1929 peak.