This article describes how sex offender registration and notification affect the frequency and incidence of offenses and checks for change in police response to reported crimes. The evidence suggests that registration reduces the frequency of sex offenses among "local" victims" (e.g., friends, acquaintances, neighbors) but not against strangers. It also presents evidence that community notification deters first-time sex offenses but increases recidivism by registered offenders by imposing social and financial costs, making non-criminal activity relatively less attractive after an initial conviction. This is consistent with previous work by criminologists and important because the stated purpose of community notification is to reduce recidivism.