The relational unconscious is the fundamental structuring property of each interpersonal relation; it permits, as well as constrains, modes of engagement specific to that dyad and influences individual subjective experience with-in the dyad. Three usages of the concept of thirdness are delineated and contrasted with the concept of the relational unconscious, which, it is suggested, has the advantage of being both consistent with existing views of unconscious processes and more directly applicable to therapeutic concerns. Enactments and intersubjective resistances are viewed as clinical manifestations of the relational unconscious, and the therapeutic action of psychoanalysis results, in part, from altering the structure of the relational unconscious that binds analysand and analyst.