October 29, 1929, is known as Black Tuesday, the climactic trading day of the Wall Street Crash.
On that day, about 16 million shares changed hands on the New York Stock Exchange, a record at the time. The Dow Jones Industrial Average fell approximately 12%, adding to the losses from the previous week. Heavy selling reflected collapsing confidence after years of speculative buying and margin-financed investment.
Black Tuesday did not single-handedly cause the Great Depression. The crash damaged wealth and confidence, while bank failures, falling demand, deflation, and policy decisions deepened the economic downturn. The market had already fallen sharply on Black Thursday, October 24, and Black Monday, October 28.
A common mix-up is treating Black Tuesday as the entire crash. It was the most famous day in a broader decline that continued into 1932, when the Dow reached its depression-era low.