Black Monday was the 1987 crash day on which the Dow Jones Industrial Average suffered its largest one-day percentage loss.
On October 19, 1987, the Dow plunged 508 points, or 22.61%. The decline occurred amid a worldwide sell-off and followed large losses in Asian and European markets. The percentage fall remains the Dow's greatest single-day decline, even though later crashes produced larger point losses because the index was much higher.
Analysts have linked the panic to elevated valuations, trade and currency tensions, investor concern about interest rates, and the rapid spread of computerized portfolio-insurance strategies. Those automated strategies could reinforce selling when prices dropped.
The crash did not lead to a depression comparable to the 1930s. The Federal Reserve, led by Chairman Alan Greenspan, announced that it was ready to serve as a source of liquidity. Exchanges also introduced circuit breakers after the event, though the modern rules have been revised several times.