Part 1: Theoretical Models of Right Brain Therapeutic Action. The first part of this article on the central role of the right brain in group psychotherapy offers evidence-based theoretical models of therapeutic action cocreated by the group members and the group leader. It describes how recent advances in interpersonal neurobiology and neuropsychoanalysis allow for a deeper understanding of the underlying nonverbal right brain change mechanisms beneath the words in individual psychotherapy. It then expands this model to the group context, specifically focusing on the theoretical constructs of cohesion, attachment, transference-countertransference dynamics, and implicit affect regulation, all of which are right brain functions. Part 1 concludes with a discussion of the fundamental role of these right brain mechanisms in synchronized group regressions and reenactments of attachment trauma that allow for new beginnings in emotional and relational development. Part 2: Clinical Case Analyses of Group Right Brain Regressive Enactments. The second part of this article offers case examples and commentary on working with early dysregulated attachment histories and the affect blunting defense of dissociation. Clinical vignettes demonstrate how the group reenacts attachment dynamics in transient regressions into an earlier stage of preverbal development, outside of the domain of language. Such emotionally shared regressions of attachment trauma, rupture, and repair allow the group members and leader to companion each other into and out of enactments. In this manner, regulated reenactments of preverbal emotional experiences potentially allow the cohesive group to expand adaptive right brain capacities to regulate and communicate a broader range of affectively charged subjective self states, thereby cocreating new ways of being with others.