The global stock-market crash that struck in October 1987 is known as Black Monday.
Black Monday refers specifically to October 19, 1987, when markets around the world fell sharply. The Dow Jones Industrial Average dropped 22.6%, its largest one-day percentage decline. Hong Kong, London, Australia, and several other markets also recorded exceptionally severe losses, showing how rapidly financial shocks could cross borders.
The sell-off followed a period of strong stock-market growth and increasing concern about trade deficits, interest rates, and valuations. Portfolio insurance programs and computer-driven selling added momentum once prices began falling. Because no single explanation fully accounts for the scale of the decline, economists continue to study the interaction of market structure and investor behavior.
The name can be confused with Black Tuesday, the major U.S. sell-off of October 29, 1929. Black Monday is the 1987 event, while Black Tuesday belongs to the Wall Street Crash of 1929. Circuit breakers introduced afterward were intended to reduce the chance of similar cascading sales.