This review explores diverse theories that provide the basis and rationale for infant mental health, a relatively new service designed to reduce social and emotional disturbances in infancy and early parenthood. Psychoanalytic theory, attachment theory, social and contextual theories, developmental theories and the work of Donald Winnicott and Daniel Stern contribute to the fundamentals of infant mental health practice, increasing the understanding of development in early childhood and the power of relationships in defining a context for social and emotional growth. Infant mental health practice influences psychotherapeutic change in early parenthood and the possibility of attachment security in early infancy.