Established in 1997 in France as a post-trial measure of sentence adjustment, electronic monitoring (EM) has rapidly grown in recent years, in the context of a prison overcrowding crisis. The first part of this article describes how EM has been extended to all phases of the criminal justice process (pre-trial, trial, post-trial, post-penal) and how diverse its uses have become as a consequence, including the implementation of GPS-EM alongside the traditional fixed system. This part also presents a statistical analysis of the monitored population. The second part presents the results of a follow-up study of a cohort of former EM convicts 5 years after release. It attempts to analyse the factors of recidivism and to compare the results with other available data. This comparison points to the fact that EM recidivism is significantly lower than that of former prisoners and comes second just after community work sentences.