Melanie Klein was born Melanie Reizes in Vienna into a Jewish family with intellectual ambitions that her circumstances would long frustrate. She was a gifted student who hoped to study medicine, but the financial difficulties following her father's death and a marriage to Arthur Klein at the age of twenty-one redirected her energies toward domesticity and frequent depression. She encountered psychoanalysis through Freud's On Dreams in 1914, sought analysis with Sándor Ferenczi in Budapest, and was drawn into the psychoanalytic movement at a time when it was beginning to consider whether children might be analysed directly. Ferenczi encouraged her to work with children, and her early clinical work with young patients produced the play technique that would become her signature contribution. She moved to Berlin in 1921 and entered analysis with Karl Abraham, whose influence on her theory of early object relations proved decisive. Invited to London by Ernest Jones in 1926, she joined the British Psycho-Analytical Society and remained in England for the rest of her life. The 1940s brought the “Controversial Discussions” between her followers and the Freudians loyal to Anna Freud, which ultimately established three separate training streams within British psychoanalysis. Klein died in London on 22 September 1960, having founded the object-relations tradition that would influence not only clinical practice but also educational theory, infant observation, and developmental psychology.

Klein's most immediately practical contribution was her development of the play technique as a method of psychoanalytic work with children from the earliest years. Rather than relying on verbal free association — the classical analytic method that required the linguistic sophistication of adults — Klein equipped her consulting room with small toys: figures, animals, vehicles, drawing materials, water, and clay. She observed that children's play, like adults' dreams, was structured by unconscious fantasy and could be interpreted according to the same principles of displacement, condensation, and symbolisation. A child who repeatedly crashed toy cars was not simply playing out a pleasurable fantasy but communicating something about aggression, anxiety, and the internal objects that populated her psychic world. Klein argued that play was the natural language of childhood, and that the analyst's task was to translate its symbolic content into interpretations accessible to the child, thereby reducing anxiety and enabling development. This insight had profound implications for nursery education and child observation, encouraging practitioners to treat children's spontaneous activity as meaningful communication rather than mere recreation.

Klein's central theoretical contribution was to relocate the foundational drama of psychic development from the Oedipal triangle of the later years — the focus of classical Freudian theory — to the earliest months of infancy and the infant's relationship with part-objects, above all the mother's breast. She argued that from birth the infant is engaged in a primitive but complex inner life structured by love, hatred, gratitude, envy, anxiety, and the defences against them. The breast is experienced not simply as a physical object but as a psychic object: when it is felt to be present and satisfying it becomes the “good breast,” an internal source of security and trust; when it is felt to be absent or frustrating it becomes the “bad breast,” an internal source of threat and persecution. This splitting of experience into good and bad is not pathological but a normal feature of early development; the developmental challenge is to move toward integration, toward the capacity to hold both the good and the bad aspects of experience as belonging to the same object. Object relations theory shifted the focus of psychoanalytic education from the resolution of Oedipal conflict toward the nurturing of the earliest relational capacities — the foundations of empathy, trust, and the ability to learn from experience.

Klein described two fundamental positions — organised ways of experiencing self, others, and the world — that the infant moves between and that continue to structure adult mental life. In the paranoid-schizoid position, experience is split: the self and the world are divided into persecutory “bad” parts and idealised “good” parts, anxieties are of a persecutory character, and relating to whole persons is not yet possible. In the depressive position, the infant begins to recognise that the good and bad aspects of experience belong to the same person — that the mother who frustrates is the same mother who satisfies — and this recognition brings a new form of anxiety, the concern that one's own hatred may have damaged the loved person. Working through the depressive position involves mourning, reparation, and the development of a concern for others as whole, separate beings. Klein saw the capacity to reach and sustain the depressive position as the foundation of moral development, creativity, and the ability to learn: learning itself requires tolerating not-knowing, accepting one's own limitations, and trusting that understanding can be recovered even after frustration and confusion.

Klein's concept of envy — the primitive attack on the goodness of the object precisely because it is experienced as good — has significant implications for educational psychology. She distinguished envy from jealousy and greed, arguing that envy is directed not at the possession of something the other has but at the very quality of goodness itself: the envious child or student wishes to spoil or destroy the good precisely because it cannot be borne that the good should reside in another. In educational terms, envy of the teacher's knowledge or authority can manifest as learning inhibitions, an inability to take in what is offered, or a compulsive need to devalue instruction. Gratitude, by contrast — the capacity to receive goodness without destroying it — is the foundation of genuine learning. Klein's analysis suggested that educational failure is not always a cognitive problem but may be rooted in early emotional experience that makes the act of receiving knowledge feel threatening, humiliating, or unbearable.

Klein's framework profoundly influenced the Tavistock Clinic's approach to infant observation, training in which was later introduced as a standard component of child psychotherapy and social work education in Britain. Her insistence on the reality of very early mental life contributed to a broader shift in developmental psychology toward taking infants seriously as psychic beings — a shift that anticipated, and in some respects prepared the ground for, later attachment theory. Her concepts were taken up by Wilfrid Bion, whose theory of the container and the contained — the idea that the mother's (and teacher's) capacity to receive and process the infant's projected anxieties is what makes thinking possible — became a cornerstone of psychoanalytically informed thinking about learning environments. For educators, the Kleinian tradition suggests that the emotional climate of the classroom, the teacher's capacity to hold and metabolise the distress, confusion, and aggression that learners project, is not peripheral to learning but constitutive of it.

• The Psycho-Analysis of Children (1932)
• Contributions to Psycho-Analysis, 1921–1945 (1948)
• Envy and Gratitude (1957)
• Narrative of a Child Analysis (1961)
• The Writings of Melanie Klein (4 volumes, 1975)