Control in the face of process input constraints is very common and of great practical importance in the processing industries. Generic Model Control (GMC) is a model-based control framework for both linear and nonlinear systems. In this paper, a constrained GMC controller tuning approach using a nonlinear;east squares technique is proposed. This tuning approach is simple to apply. For a SISO GMC control system with input saturation, the tracking performance is significantly improved by adding a simple heuristic switching strategy. The effectiveness of the proposed controller tuning approach is demonstrated using dynamic simulations and MIMO real-time experiments.