The problem of controlling processes with a wide range of operating conditions is addressed. The process dynamics is represented by the weighted-sum of the linear model by using model validity functions. By treating the validity functions as uncertainties in the system, an internal model control (IMC) design strategy is developed for a particular class of nonlinear systems. Robust stability analysis under mixed time-varying and time-invariant uncertainties is presented. Simulation results confirm that the proposed IMC design method is indeed superior to its conventional counterpart.