Rules for the regulation of medical devices, such as hip prostheses and implantable defibrillators, are complex and differ from those for drugs. Aaron Kesselheim, MD, JD, MPH, and Jonathan Darrow, SJD, LLM, JD, MBA, both faculty members in the Division of Pharmacoepidemiology and Pharmacoeconomics at Brigham & Women’s Hospital, review device classes and approval pathways used by the US Food and Drug Administration (FDA), and prospects for improvements and reform in the agency’s processes. Related Article(s): FDA Regulation and Approval of Medical Devices