Dr. Ida Sim is Professor of Medicine at the University of California San Francisco (UCSF), Director of Digital Health for the Division of General Internal Medicine, and codirector, Informatics and Research Innovation at UCSF’s Clinical and Translational Sciences Institute. Stephen Morrissey, the interviewer, is the Executive Managing Editor of the Journal. I. Sim. Mobile Devices and Health. N Engl J Med 2019;381:956-968.