Design rarely proceeds linearly. We compare human-centered models (IDEO, Double Diamond, d.school) with engineering and new product development (NPD) frameworks (Pahl & Beitz, V-model, Stage-Gate, Lean Startup), then situate AI-augmented cycles (Double Hump) that widen search and tighten evidence loops. The chapter equips readers to select and hybridize processes based on uncertainty and cost of late change, emphasizing cadence (divergence/convergence), accountability at gates, and the importance of process literacy over one-size-fits-all prescriptions.