This handbook reviews promising applications of psychedelics in treatment of such challenging psychiatric problems as posttraumatic stress disorder, major depression, substance use disorders, and end-of-life anxiety. Experts from multiple disciplines synthesize current knowledge on psilocybin, MDMA, ketamine, and other medical hallucinogens. The volume comprehensively examines these substances’ neurobiological mechanisms, clinical effects, therapeutic potential, risks, and anthropological and historical contexts. Coverage ranges from basic science to practical clinical considerations, including patient screening and selection, dosages and routes of administration, how psychedelic-assisted sessions are structured and conducted, and management of adverse reactions.