This textbook evolved from our experience editing the Comprehensive Textbook of Psychiatry. That book is nearly 4,000 double-column pages long, with more than 450 contributions by outstanding psychiatrists and behavioral scientists. It serves the needs of those who require an exhaustive, detailed, and encyclopedic survey of the entire Oeld. In an ePort to be as comprehensive as possible, the textbook spans two volumes to cover the material, clearly rendering it unwieldy for some groups, especially medical students, who need a brief and more condensed statement of the Oeld of psychiatry. To accomplish this, sections of the Comprehensive Textbook of Psychiatry were deleted or condensed, new subjects were introduced, and all sections were brought up to date, especially certain key areas, such as psychopharmacology. We wish to acknowledge our great and obvious debt to the more than 2,000 contributors to the current and previous editions of the Comprehensive Textbook of Psychiatry, all of whom have allowed us to synopsize their work. At the same time, we must accept responsibility for the modifications and changes in the new work.