Margaret Mahler (1897–1985) was a Hungarian-born psychoanalyst who immigrated to the United States in 1938. In 1975, she published a book with Anni Bergman and Fred Pine called the Psychological Birth of the Human Infant. This book was very influential in psychoanalytic circles because of its use of the direct observation of children. In other words, Mahler applied the scientific method to clinical theory, some thing few psychoanalytic theorists had bothered to do previously. Mahler was roughly contemporary with John Bowlby and Mary Ainsworth, the founders of attachment theory, who were also pioneers in this domain.

Like many psychoanalysts of her time, Mahler believed that the foundation of adult personality was created in the childhood relationship with the mother. Mahler was focused on independence, how the child grows from an entirely dependent being to one who is relatively independent, both physically and psychologically. She called this developmental process separation-individuation. Mahler was most interested in the child’s growing ability to recognize both the self and the mother as independent and separate beings. It is the child’s developing capacity to represent (or conceptualize) the mother that allows independence from the mother. When children can think about their mother when she is not there, they can comfort themselves with the memory of her presence. In Mahler’s terms, the child has internalized the mother.