Morton Prince, a debonair Boston neurologist, established the modern American tradition of psychopathology and psychotherapy in the closing decade of the nineteenth century. Born in 1854, two years before Sigmund Freud and five years before Pierre Janet, he criticized and adapted their work to his own particular interests, which were primarily the exploration of hypnosis, multiple personality, and the unconscious. Prince informally headed the most sophisticated group of psychopathologists in the English-speaking world, which flourished in Boston and Cambridge beginning around 1890. He founded the Journal of Abnormal Psychology in 1906 and the American Psychopathological Association in 1910. The essays in this volume have been chosen by Nathan G. Hale, Jr., to illustrate four major stages in Prince's career. The first, from 1885 to 1898, saw his development of a dynamic psychotherapy, based on the existence of unconscious mental processes. During the second period, from 1898 through 1911, he made intensive studies of multiple personality. In the third, from 1909 through 1924, he confronted psychoanalysis and behaviorism. During the last period, from about 1914 through 1927, he published his final views of the unconscious, hypnotism, and personality. Morton Prince's observations remain important partly because they are so richly detailed, partly because of their dramatic and human interest, but chiefly because they shed light on phenomena that still defy final explanation.