Great article summarizing the causes of the stock market crash of '29 and '87 (mostly the '87 crash). Pay close attention to the historical PE ratios graph.  Also, the following question leaves a lot to think about:  "When is a crash a buying opportunity?"  In '87 it was a great opportunity because the economy's fundamentals were strong so there was nothing but upside.  In '29 they weren't because the economy was going into a recession (easy to say in hindsight).   How does that relate the situation today?   I'm a strong believer that we are bound to see a crash in the very near future, but that it won't be a buying opportunity.  We have yet to feel the full effects of the housing market and that will keep the economy soft for at least 2 more years.  The buying opportunity will come but it won't be until some point towards the end of 2008, early 2009.  Then again, there are exceptions:  buy GOOG now ($650) if you want a 20% annualized return in the next 24 months (YES, you math wizzes out there. $1000+), but be prepared a rollercoaster ride from hell.