Mahler's developmental theories are reviewed in the light of subsequent clinical experience and theoretical and empirical critique. Several modifications are proposed, each tending to particularize and focus the nature and scope of developmental events. Particular attention is accorded the “symbiosis” concept, and focus placed on transmission of psychodynamic issues from mother to infant and on the progressive buildup of self-sustaining pathological systems. Overall, an argument is advanced for the continued developmental import of Mahler's “symbiotic” and “separation-individuation” phase formulations, though with recognition of significant individual differences in their role in individual lives. An argument is advanced also for the clinical utility of these ideas, and illustrations presented, though the link between clinical applications and psychoanalytic theories of early development remains problematic.