Black Monday, October 19, 1987, marked the biggest one-day percentage fall in U.S. stock-market history.
On that Monday, the Dow Jones Industrial Average dropped 508 points, or 22.6 percent. The percentage fall exceeded the worst single-day decline during the 1929 crash. Stock markets in other countries also suffered severe losses, making the event a genuinely global crash rather than an isolated Wall Street disturbance.
Several factors were discussed afterward, including high valuations, concerns about economic conditions, international trade tensions, and computerized portfolio-insurance strategies. Those automated strategies could intensify selling when prices fell, although no single explanation fully accounts for the crash.
The crash did not lead to a depression comparable to the 1930s. The Federal Reserve supplied liquidity, and markets eventually recovered. Black Monday is also distinct from the 1929 Black Monday, a term sometimes used for October 28, 1929.