Action systems, as the depth-psychology corpus deploys this term, designates a family of psychobiologically grounded, evolutionarily conserved motivational programs that organize perception, affect, cognition, and movement toward species-typical goals. The concept acquires its most systematic elaboration in the trauma literature, particularly in Ogden’s sensorimotor framework and Van der Hart’s structural-dissociation model, where action systems function as the neural and behavioral substrate that mediates both adaptive daily life and defensive survival responses. The central theoretical tension in this literature concerns the relationship between the systems of ordinary living—attachment, exploration, play, caregiving, energy regulation, sexuality—and the defensive subsystems mobilized by threat. In traumatized individuals, chronic activation of defensive action systems displaces the systems of daily life, producing the biphasic symptom pattern of intrusion and avoidance that defines trauma-related disorders. Van der Hart and colleagues extend this framework to explain how structural dissociation partitions the personality along action-system lines, with apparently normal parts organized around daily-life systems and emotional parts anchored in defensive systems. Ogden foregrounds the somatic dimension, tracing how action tendencies express themselves as preparatory motor responses and incomplete physical movements. The concept thus bridges evolutionary biology, neuroscience, attachment theory, and clinical phenomenology, and stands as a foundational construct for understanding both the architecture of dissociation and the goals of somatic and integrative treatment.