Public outrage over crime has found political expression in the proposal and enactment of various laws mandating lengthy sentences for repeat felons. Put forward under the slogan, "three strikes and you're out," these laws generally prescribe that felons found guilty of a third serious crime be locked up for 25 years to life. California's Three Strikes law went into effect in March 1994 and is rather comprehensive. Although the first two strikes accrue for serious felonies, the crime that triggers the life sentence can be any felony. Further, California's law doubles sentences for a second strike, requires that extended sentences be served in prison, and limits good time earned during prison to 20 percent of the sentence imposed. A cost-benefit analysis projects that the law will reduce serious felonies committed by adults in California by 22 to 34 percent. About a third of felonies eliminated will be violent crimes such as murder, rape, and assaults causing great bodily injury. This reduction in crime will be achieved at a cost of $4.5 to $6.5 billion more per year. Criticisms of California's Three Strikes law and possible alternatives are noted. The authors point out that cost-effectiveness is not always the most important criterion in crime control. Supplemental information on the economic analysis of the Three Strikes law is contained in appendixes. 17 references, 23 tables, and 19 figures