In the United States, 250,000 people die from a cardiac arrest every year. Despite a well established emergency medical response system, survival from out-of-hospital cardiac arrest remains poor in United States cities. Paramount to achieving successful resuscitation of a cardiac arrest victim is provision of early defibrillation. Among patients that arrest due to a ventricular fibrillation, the likelihood of survival decreases by 10% for every minute of delay in defibrillation. In 1995, the American Heart Association challenged the medical industry to develop a defibrillator that could be placed in public settings, used safely by lay responders, and provide earlier defibrillation to cardiac arrest victims. Over the last decade, there have been significant technological advancements in automated external defibrillators (AEDs), and clinical studies have demonstrated their benefits and limitations in various public locations. This article discusses the technologic features of the modern AED and the current data available on the use of AEDs in public settings.