Psychoanalysis is a psychological and psychotherapeutic theory conceived in the late 19th and early 20th centuries by Austrian neurologist Sigmund Freud. Psychoanalysis has expanded, been criticized and developed in different directions, mostly by some of Freud's former students, such as Alfred Adler and Carl Gustav Jung, Wilhelm Reich and later by neo-Freudians such as Erich Fromm, Karen Horney, Harry Stack Sullivan and Jacques Lacan.