Electronic monitoring (EM) is a way of supervising offenders in the community whilst they are on bail, serving a community sentence or after release from prison. Various technologies can be used, including voice verification, GPS satellite tracking and - most commonly - the use of radio frequency to monitor house arrest. It originated in the USA in the 1980s and has spread to over 30 countries since then. This book explores the development of EM in a number of countries to give some indication of the diverse ways it has been utilized and of the complex politics which surrounds its use. A techno-utopian impulse underpins the origins of EM and has remained latent in its subsequent development elsewhere in the world, despite recognition that is it less capable of effecting penal transformations than its champions have hoped. This book devotes substantive chapters to the issues of privatisation, evaluation, offender perspectives and ethics. Whilst normatively more committed to the Swedish model, the book acknowledges that this may not represent the future of EM, whose untrammelled, commercially-driven development could have very alarming consequences for criminal justice. Both utopian and dystopian hopes have been invested in EM, but research on its impact is ambivalent and fragmented, and EM remains undertheorised, empirically and ethically. This book seeks to redress this by providing academics, policy audiences and practitioners with the intellectual resources to understand and address the challenges which EM poses.