The Dow Jones Industrial Average suffered its largest one-day percentage drop on 19 October 1987, known as Black Monday.
The Dow fell 508 points, or 22.6%, in a single trading session. The decline was part of a worldwide stock-market collapse that also affected markets in Europe, Asia, and Australia. Although the point loss has since been surpassed, the percentage fall remains a major benchmark in market history.
Several factors contributed, including high valuations, rising interest rates, trade tensions, and computerized portfolio-insurance selling. Automated trading accelerated the selling once prices began to fall. The crash did not immediately produce a depression like the 1930s collapse, but it changed financial regulation and market structure.
The date is sometimes confused with the 1929 Wall Street Crash, whose most famous sessions occurred nearly six decades earlier. Central banks and exchanges introduced safeguards after 1987, including circuit breakers designed to pause trading during severe declines.