In this paper the author takes a close look at Benjamin Wolstein's chapter, ‘Therapy’, from his book, Countertransference, published in 1959. This chapter contains a discussion of what he refers to as the interlock between analyst and patient, or today what we might describe as transference/countertransference enactment. The author shows how Wolstein's concept of the interlock and its relation to the analyst's countertransference was radical and innovative for its time. Wolstein's notion of a transference/countertransference interlock, along with the seminal contributions of Ferenczi and some of the early interpersonal theorists, anticipates the complexities of a two-person psychology and the entanglement which can occur from the intermingling of unconscious processes of analyst and patient in the experiential field. The author highlights three main ideas. First, the author provides a brief review of enactment with an emphasis on the role of the analyst's participation as conceptualized by the various theoretical perspectives. An historical context is given for Wolstein's clinical theorizing. Second, the author explicates Wolstein's concept of the interlock, with particular attention to the processes involved which account for the complexities it presents. Third, the author examines the ‘working through’ process, including the emergence of intersubjectivity in the resolution of the interlock. The author shows throughout Wolstein's emphasis on the influence of the analyst's personal psychology, mutuality, and intersubjectivity, all of which anticipated the gradual interpersonalization of psychoanalysis across the various schools of thought.