The first day of the 1929 Wall Street crash, when the Dow fell about 13%, was Black Monday.
On October 28, 1929, the Dow Jones Industrial Average declined about 12.8%, making Black Monday the first of two catastrophic sessions in the week. The following day, October 29, became known as Black Tuesday and brought another severe fall. Together, the sessions destroyed enormous amounts of paper wealth and intensified public fear.
The crash followed years of speculative buying, widespread use of margin, and rapid expansion in share prices. It did not by itself create every condition of the Great Depression, but it damaged confidence and contributed to a broader contraction in investment, production, and employment. Black Monday is sometimes confused with the 1987 crash because both dates share the name; the year and surrounding event are essential to identifying which episode is meant.