A number of methods have been proposed and implemented for keeping track of sex offenders who have been released into the community. Among these methods are mandatory sex offender registration and the establishment of “pedophile-free zones” around such places as schools and playgrounds. The problems with such methods are identified and include offender noncompliance with mandatory registration laws and constitutional issues involved with the enforced isolation of sex offender populations. GPS systems, on the other hand, offer a technologically advanced method of tracking the movements of sex offenders that is more difficult for offenders to circumvent. The technological components of GPS systems are described and include a small transmitter that is generally worn on the ankle, a portable tracking device (PTD) that must be carried by the offender or be near the offender at all times, and a charging unit for the PTD that is stationed at the offender’s residence. The use of the GPS system for tracking offenders involves setting up permitted and forbidden offender zones using a computer program, which then alerts the authorities when offenders enter forbidden zones or leave permitted zones, such as their place of employment, at unusual times. The effectiveness and limitations of GPS monitoring systems are listed and include the advantage of real-time tracking of offender locations but with the limitation of only being able to track offenders in outside locations--GPS signaling cannot track offenders inside large buildings, inside subways or tunnels, in heavily wooded areas, or in areas shielded by metal. The types of offender populations most likely to be supervised with GPS technology include sex offenders, domestic violence offenders, post-work release offenders, and house arrest offenders. Finally, information is offered about the cost of GPS systems, which represents a considerable savings over incarceration.