Many countries have recently adopted electronic monitoring (EM) as an alternative sentence in order to reduce incarceration while maintaining public safety. However, the empirical evidence on the effects of EM on recidivism (relative to prison) is very scarce worldwide. In this paper, we adress this debated question using quasi-experimental data from France. Our empirical strategy exploits the incremental roll-in of electronic monitoring in France, which started as a local experiment in four courts in 2000-2001, and was later adopted by more and more courts (2002-2003). Our IV estimates show that fully converting prison sentences into electronic monitoring has long-lasting beneficial effects on recidivism, with estimated reductions in probability of reconviction of 6-7 percentage points (9-11%) after five years. There is also evidence that, in case of recidivism, EM leads to less serious offenses compared to prison. These beneficial effects are particularly strong on electronically monitored offenders who received control visits at home from correctional officers, were obliged to work while under EM, and had already experienced prison before. This pattern suggests that both rehabilitation and deterrence are important factors in reducing long-term recidivism, and that electronic monitoring can be a very cost-effective alternative to short prison sentences. However, the massive development of EM in France in recent years, with shorter and less intensive supervision, may reduce its effectiveness.