Black Monday refers to October 19th 1987, the culmination of a violent market downswing that had begun days before and when US stock markets experienced their biggest-ever single-day loss. This precipitated a global sell-off, which was amplified by automated sell orders from program trading and by derivatives. The Dow Jones Industrial Average stock index fell 23% and the S&P 500 by 20%. However, the severe market declines were only a minor give-back, as the Dow had risen by over 250% in the previous five years and stock markets were seen as heavily over-valued. The lows of October 1987 acted as a buying signal and the market resumed its upward trajectory until the dot.com crash of 1999/2000.