In 1994, California voters passed legislation enacting the “Three Strikes” law. If you are convicted of any felony after having two previous “serious” or “violent” felonies, you face a mandatory sentence of 25 to life in state prison. If you have one previous “strike” conviction, any sentence you get on a new felony will be doubled. Despite what many people think, not every felony counts as a strike. For example, if you are convicted twice for simple drug possession (a non-strike offense), your next felony would not be a “third strike” that would result in a life sentence. [But keep in mind that other provisions of the California Penal Code may affect your sentence dramatically.] If you are accused of any crime of violence, the best advice is to seek legal representation to possibly avoid a “three strikes” situation.
Edited November 8, 2012:
With the passage of Proposition 36 by the voters, in order for a “third strike” case to result in a 25 to life sentence, a person must have 2 prior qualifying “strikes” and the current offense must also be a “serious” or “violent” offense. Serious offenses are listed in Penal Code section 1192.7(c) and violent offenses are listed in Penal Code 667.5(c)