Objective: The objective of this study was to estimate the benefits and costs of using electronic monitoring (EM) and home detention to reduce crime committed by parolees and probationers. Method: Data from a national survey of state prison inmates was adjusted and used to estimate the number of crimes that would have been committed by all parolees and probationers over the course of one year in the absence of EM and home detention. The data were analyzed in combination with existing analyses of the effectiveness and costs of EM and home detention and the economic costs of crime to estimate the benefit-cost ratio of nationwide implementation of EM and home detention with all parolees and probationers. Results: EM plus home detention could avert an estimated 781,383 crimes every year. The social value of the annual reduction in crime is $481.1. billion. Society would gain $12.70 for every dollar expended on the proposed intervention. Conclusion: EM plus home detention could be an effective deterrent to crime and could have enormous social benefits, especially if it is applied early and saves what would otherwise be habitual offenders from a life of crime.