Background: The Public Access Defibrillation (PAD) Trial was a randomized, controlled trial designed to measure survival to hospital discharge following out-of-hospital cardiac arrest (OOH-CA) in community facilities trained and equipped to provide PAD, compared with community facilities trained to provide cardiopulmonary resuscitation (CPR) without any capacity for defibrillation. Objectives: To report the implementation of community-based lay responder emergency response programs in 1,260 participating facilities recruited for the PAD Trial in the United States and Canada. Methods: This was a descriptive study of the characteristics of participating facilities, volunteers, and automated external defibrillator (AED) placements compiled by the PAD Trial, and a qualitative study of factors that facilitated or impeded implementation of emergency lay responder programs using focus groups of PAD Trial site coordinators. Results: The PAD Trial enrolled 1,260 community facilities (14.8% residential), with 20,400 lay volunteers (mean ± standard deviation = 13.4 ± 10.7 per facility) trained to respond to OOH-CA. The 598 locations randomized to receive AEDs required 2.7 ± 1.8 AEDs per facility. Volunteer attrition was high, 36% after two years. Barriers to recruitment and implementation included identification of appropriate "at-risk" facilities, lack of interest or fear of litigation by a facility key decision maker, lack of motivated potential volunteer responders, training and retraining resource requirements, and lack of an existing communication/response infrastructure. Conclusions: These data indicate that implementation of community-based lay responder programs is feasible in many types of facilities, although these programs require substantial resources and commitment, and many barriers to implementation of effective PAD programs exist.