Born in Vienna, the youngest daughter of a dentist, Klein originally planned to study medicine. However, she abandoned her plans when, aged 21, she married (which, although unhappy, produced three children). Klein became a key figure in the development of psychoanalytic theory following her analysis with Sandor Ferenczi, an associate of Sigmund Freud. Her interests lay mostly in the mental life of children and babies, unlike Freud's interest in adults. However, her particular theoretical ideas brought her into conflict with Anna Freud, Sigmund's daughter, who also focused on personality development in children, but did not agree that children could be psychoanalysed. She invented 'play therapy', using small dolls and objects to evoke symbolic play by children. Her theoretical ideas have been highly influential in some schools of psychoanalytic thought and more recently have been taken up by some feminist and post-modern theorists. She is perhaps best known as the originator of the ideas underlying object relations theory, particularly the concepts of projective identification, and schizoid and depressive positions. She left Austria and came to London, to the Tavistock clinic, in 1926.