Material Engagement, as it surfaces across the depth-psychology corpus, names the encounter between the psyche and concrete physical substrates — art media, bodily sensation, somatic resources, and the tactile surround of therapeutic space — as a primary vehicle of psychological transformation. The term does not appear with uniform theoretical elaboration; rather, it emerges obliquely across several traditions. In expressive arts therapy (McNiff), the material world of paint, water, and sailboats becomes a mediating third through which the psyche accesses subliminal aesthetic and healing forces. In sensorimotor and trauma-oriented approaches (Ogden), physical objects and somatic resources — the teddy bear, the texture of tissue — constitute genuinely therapeutic agents alongside relational ones. The polyvagal framework (Porges, Dana) complicates the term by distinguishing between material things, which cannot themselves cue safety, and the prosodic and kinesthetic signals that activate the social engagement system. This tension — between the inert object and the animate, felt encounter — runs throughout the corpus. Yalom situates engagement as the existential remedy for meaninglessness, though his usage remains phenomenological rather than material. The convergence of these positions suggests that material engagement is understood less as passive contact with matter and more as a mode of attunement whereby the organism’s homeostatic and meaning-making processes are recruited through tangible, sensory interaction with the world.