The stock market meltdown of Oct. 19, 1987--in which the Dow plunged 22.6%, its worst one-day percentage loss since the crash of 1929--was a big jolt for both Wall Street and Main Street. Although it was 20 years ago, the 1987 plunge remains a vivid memory, which makes this the right time for BusinessWeek.com to examine what has changed since that day. What lessons have we learned? Could it happen again? Plus: A slide show in which Wall Street pros share their recollections of that day and offer insights into its impact on today's markets. Go to businessweek.com/investing for all this and more.