Black Tuesday, the most famous session of the 1929 Wall Street crash, occurred on October 29, 1929.
On that day, roughly 16 million shares changed hands on the New York Stock Exchange, setting a trading-volume record at the time. Prices collapsed after heavy selling, following severe declines on Black Thursday, October 24, and Black Monday, October 28.
The crash did not cause the Great Depression by itself, but it became its best-known financial symbol. The broader economic downturn involved bank failures, falling production, deflation, unemployment, and reduced international trade.
A common mix-up is treating Black Tuesday as the entire crash. The market continued falling after October 29, and the Dow Jones Industrial Average did not reach its ultimate low until July 1932.