Black Monday began on October 19, 1987, when the Dow Jones Industrial Average fell 22.6 percent in one session.
The plunge was the largest one-day percentage decline in the Dow's history. Selling spread rapidly across international markets, with major losses in places including Hong Kong, London, and Australia. The worldwide nature of the event made it one of the most recognizable modern stock-market crashes.
Several factors were associated with the fall, including overvalued markets, worries about interest rates and trade deficits, and computerized portfolio-insurance selling. These explanations are not identical to a single confirmed cause, because market crashes usually result from interacting pressures rather than one trigger.
Black Monday is often confused with Black Monday in 1929, which occurred on October 28. The 1987 event is also distinct from Black Tuesday, the famous October 29 session in the 1929 crash.