Black Monday occurred on October 19, 1987, when global share prices suffered an exceptionally severe one-day collapse.
The Dow Jones Industrial Average fell 508 points, or 22.6%, in a single session. That percentage loss remains the largest one-day percentage decline in the Dow’s history. Markets in Hong Kong, London, Australia, and other financial centers also plunged, making the event international rather than solely American.
Several forces contributed, including investor anxiety about trade deficits and interest rates, computerized trading strategies, and portfolio-insurance programs that automatically sold futures as prices fell. These mechanisms amplified the selling, although historians and economists do not identify one universally accepted single cause.
Black Monday is sometimes confused with Black Tuesday of 1929, but the two crashes occurred nearly 58 years apart. The 1987 episode also differed from 1929 because the broader financial system remained intact and markets eventually recovered. Regulators later introduced circuit breakers to pause trading during extreme price movements.