Timothy Petersen, PhD is a clinical psychologist in the Department of Psychiatry at Mass General and an Assistant Professor of Psychiatry at Harvard Medical School. Clinically he focuses on using cognitive behaviorally based interventions for difficult to treat mood disorders. His research has included the seminal NIH Sequential Treatment Alternatives to Relieve Depression (STAR*D) investigation, as well as studies investigating psychotherapeutic interventions to reduce relapse in those with mood disorders.