The treatment of many mental health disorders—including depression, anxiety, attention-deficit/hyperactivity disorder, or autism—often involves a sequential, individualized approach whereby treatment is adapted repeatedly in response to the changing health status or context of the individual. An adaptive intervention is a sequence of individually tailored decision rules that help guide whether and how to provide treatment and what type of treatment to provide at critical decision points in the course of care. The sequential, multiple-assignment, randomized trial (SMART) is a multistage, factorial, randomized trial design that can be used by scientists to develop empirically supported adaptive interventions.