This chapter repositions aggression within Gestalt therapy as a boundary phenomenon with distinct forms—invasion, violence, and destructiveness—rather than a synonym for cruelty. After noting historical drifts (Perls’ emphasis on “dental” aggression and the later minimization of sexuality and other aggressive modes), the authors trace how psychoanalysis set up an antithesis between sexuality and aggression, which Gestalt reframed as complementary life processes. They introduce “sexual aggression” as a creative adjustment: the effective use of assertive force supported by a ground of love, desire, and creativity, allowing one to take and refuse without harming self or other. Aggression is shown to depend on field conditions and, ethically, to hinge more on the how than the what of pursuing needs. Invasion names unintentional boundary-crossing that can be repaired by stepping back; violence is deliberate overstepping that persists despite protest and may range from biologically rooted taking to delinquent abuse; destructiveness is the necessary deconstruction that makes assimilation possible—now requiring greater care given today’s fragile grounds. Clarifying “contact” as awareness and action toward assimilable novelty (and rejection of the non-assimilable), the chapter argues that aggression is value-neutral until owned: adult responsibility is the capacity to choose forms of force that sustain contact, autonomy, and growth within a complex, co-constructed field.