The different phases in a bubble are backed up by 500 years of economic history. Each time the situation is obviously different, but there are always a lot of similarities. The situation applies pretty well to the current real estate bubble, which is rapidly unfolding as these lines are written.

Simplistically four phases can be identified:
1) Stealth. Those who understand the new fundamentals realize an emerging opportunity for substantial future appreciation, but at a substantial risk since their assumptions are so far unproven. So the "smart money" gets in, often quietly and cautiously. This category of investor tends to have better access to information and a higher capacity to understand it. Prices gradually increase, but often completely unnoticed by the general population. Larger and larger positions are established as the smart money start to better understand that the fundamentals are well grounded and that this asset is likely to experience significant future valuations.

2) Awareness. Many investors start to realize the momentum, bringing additional money in and pushing prices higher. There can be a short-lived sell off phase taking place as a few investors cash in their first profits (there could also be several sell off phases, each beginning at an higher level than the previous one). The smart money takes this opportunity to reinforce its existing positions In the later stages of this phase the media starts to notice and those getting in are increasingly "unsophisticated".

3) Mania. Everyone is noticing that prices are going up and the public jumps in for this "investment opportunity of a lifetime". The expectation of future appreciation becomes a "no brainer" and a linear inference mentality sets in; future prices are a "guaranteed" extrapolation of past price appreciation, which of course goes against any conventional wisdom. This phase is however not about logic. Floods of money come in creating even greater expectations and pushing prices to stratospheric levels. The higher the price, the more investments pour in. Fairly unnoticed from the general public caught in this new frenzy, the smart money as well as many institutional investors are quietly pulling out and selling their assets to eager future bag holders. Unbiased opinion about the fundamentals becomes increasingly difficult to find as many players are heavily invested and have every interest to keep the appreciation - "the game" - going. The market gradually becomes more exuberant as "paper fortunes" are made and greed sets in. Everyone tries to jump in and new investors have absolutely no understanding of the market, its dynamic and fundamentals. Prices are simply bid up with all financial means possible, particularly leverage and debt. If the bubble is linked with lax sources of credit, then it will endure far longer than many observers would expect. At some point statements are made about entirely new fundamentals implying that a "permanent high plateau" has been reached to justify future price increases; the bubble is about to collapse.

4) Blow-off. A moment of epiphany (a trigger) arrives and everyone roughly at the same time realize that the situation has changed (like the Road Runner Coyote realizing he is about to fall after walking on air for a few seconds). Confidence and expectations encounter a paradigm shift, call it a reality check, not without a phase of denial where many try to reassure the public that this is just a temporary setback and that anyone saying otherwise does not know what he is talking about. Some are fooled, but not for long. Like a directionless herd many try to unload their assets to a greater fool, but takers are few; everyone is expecting further price declines. The house of cards collapses under its own weight and late comers (commonly the general public) are left to hold the bag while the smart money has pulled out a long time ago. Prices plummet at a rate much faster than the one that inflated the bubble. Many over-leveraged bag holders go bankrupt, triggering additional waves of sales. There is even the possibility that the valuation undershoots the long term mean, implying a significant buying opportunity. However, the general public at this point considers this sector as "the worst possible investment one can make in his life". This is the time when the smart money starts acquiring assets at bargain bottom prices.

Bubbles can be very damaging, especially for those who arrived late with the hope of getting something for nothing. Even if they are inflationary events, the outcome of a bubble's blow off is very deflationary as large quantities of capital vanish in the wave of bankruptcies they trigger. Historically, they tended to be far in-between, but over the last decade we have experienced the largest bubbles in human history back-to-back; the stock market (which deflated in 2000) and the real estate (which is likely to deflate in 2006).

Source: Bubbles, Manias & Bears