Clinical ventricular tachycardia and ventricular fibrillation are associated with a high recurrence rate, and through the 1980s and the early 1990s a variety of therapies have been proposed including the implantable cardioverter defibrillator (ICD). Over the past decade it has been recognized that prospective randomized trials are imperative if the proper role for any therapy is to be defined. The Antiarrhythmic Versus Implantable Defibrillator (AVID) trial recently was concluded and helped define the role of the ICD in high-risk patients. Other trials are studying patients at high risk for sudden death who have not yet had a clinical event. The recently concluded Multicenter Automatic Defibrillator Implantation Trial and CABG Patch Trial helped determine the proper role of the ICD in various pre-event high-risk subsets. These trials are summarized in detail.