Implantable defibrillators have become the dominant therapeutic modality for patients with life-threatening ventricular arrhythmias. Current defibrillators are small (<60 mL) and implanted with techniques similar to standard pacemakers. They provide high-energy shocks for ventricular fibrillation and rapid ventricular tachycardia, antitachycardia pacing for monomorphic ventricular tachycardia, as well as antibradycardia pacing. Newer devices incorporating an atrial lead allow dual-chamber pacing and better discrimination between ventricular and supraventricular tachyarrhythmias. Randomized controlled trials have shown superior survival with implantable defibrillators than with antiarrhythmic drugs in survivors of life-threatening ventricular tachyarrhythmias and in high-risk patients with coronary artery disease. Complications associated with implantable defibrillator therapy include infection, lead failure, and spurious shocks for supraventricular tachyarrhythmias. Most patients adapt well to living with an implantable defibrillator, although driving often has to be restricted. Limited evidence suggests that implantable defibrillator therapy is cost-effective when compared with other widely accepted treatments. The use of implantable defibrillators is likely to continue to expand in the future. Ongoing clinical trials will define further prophylactic indications of the implantable defibrillator and clarify its cost-effectiveness ratio in different clinical settings.