Black Monday was the 1987 market crash that produced the largest one-day percentage decline in the Dow Jones Industrial Average.
On October 19, 1987, the Dow Jones Industrial Average dropped 22.6%, or 508 points. Although earlier crashes produced larger losses when measured over several days or in inflation-adjusted terms, no single trading day has matched that percentage fall in the Dow.
The decline was part of a worldwide sell-off. Markets in Hong Kong, Europe, Australia, and elsewhere also plunged. Analysts have linked the event to elevated valuations, macroeconomic concerns, and trading systems that automatically sold futures or shares as prices weakened.
The crash led exchanges and regulators to develop circuit breakers, which can temporarily halt trading after unusually large moves. Black Monday is distinct from the 1929 Wall Street Crash, despite the shared nickname and the fact that both involved dramatic October declines.