What are process gain, time constant, and dead time, and how do they affect control?

Process gain (Kp): output change / input change at steady state - determines controller gain requirement (high Kp needs lower controller gain). Time constant (tau): time for 63.2% response to step change - determines how fast process responds, affects integral time. Dead time (theta): delay before process starts responding - most problematic, limits achievable control performance. Control difficulty increases with theta/tau ratio. Dead time requires predictive action but derivative amplifies noise. Long dead time often needs Smith Predictor or MPC approaches.