The foundation of the Kleinian School is Freudianism extended and modified by Melanie Klein. This essay covers Klein’s contributions to: understanding early stages of the Oedipus complex and superego formation, early operation of introjective and projective mechanism, the concepts of paranoid-schizoid and depressive positions, and the importance of a very early form of envy, and the development of the Kleinian School. (28 pp.)