Additional Contributions: The following Partners Information Systems personnel were involved in developing this intervention: Barry Blumenfeld, MD, Cheryl Van Putten, PMP, John Poikonen, BA, Eric Godlewski, BA, Linda Moroni, MBA, Michael McNamara, BA, Sandra Smith, BA, Marilyn Paterno, MBI, Daniel Fuchs, BS, Oliver James, BS, and Greg Rath, BA. The BWH medication reconciliation implementation team included Erin Graydon-Baker, MS, RRT, Christine McCormack, BA, Christina Pelletier, BA, Emily Maher, MD, Ellen Bergeron, RN, MSN, Jennifer Kuzemchak, BA, Michael Cotugno, RPh, and Andrea Giannattasio, BA). The Massachusetts General Hospital medication reconciliation implementation team included George Baker, MD, Sally Millar, RN, and Margaret Clapp, BA. Bonnie Greenwood, Pharm D, and Trisha LaPointe, Pharm D, BCPS, assisted in pharmacist data collection; and BWH personnel John Orav, PhD, provided for biostatistical assistance, Elisabeth Burdick, MS, assisted in statistical programming, Amy Bloom, MPH, assisted in project management, and Emily Barsky, BA, Eric Tomasini, BA, and Emily Dattwyler, BA, provided research assistance. Jaylyn Olivo and Jeanne Zimmerman at BWH provided editorial assistance.