STOPP (Screening Tool of Older Persons’ Prescriptions) and START (Screening Tool to Alert to Right Treatment) criteria are used to identify potentially inappropriate prescribing in older adults. This article describes the consensus process to update and validate the third version of the STOPP/START criteria using evidence from a systematic review and input from a panel with expertise in geriatric pharmacology. The consensus process resulted in additional STOPP criteria (133 versus 80 in version 2) and START criteria (57 versus 34 in version 2). The additional criteria in version 3 can help clinicians detect and prevent adverse drug-drug and drug-disease interactions.