Book excerpt: Implantable cardioverter-defibrillators (ICDs) are electronic devices installed in the chest to prevent sudden death caused by abnormally fast heart rhythms. Cardiac electrophysiologists are the physicians usually responsible for implanting and maintaining these devices. The technology for ICDs is rapidly evolving, and the articles in this issue will help electrophysiologists to keep up to date with the current generation of ICDs, including selection of patients who are appropriate for the device, monitoring patients after the device is implanted, and troubleshooting problems with the device.