Mahler's theory of symbiosis and separation-individuation demonstrates the essential unity of drive, ego, and object relations psychologies. By highlighting the role that early dyadic relations play in psychic structure formation, her theory expands the understanding of human psychic development and its failures. This paper reviews Mahler's propositions and underscores their clinical importance by describing two cases where much preoedipal reconstructive work preceded the emergence of an analyzable oedipal transference neurosis.