Abstract: A system for adaptively controlling a wide variety of complex processes, despite changes in process parameters and despite both sudden and systematic drifts in the process, uses response surfaces described by quadratic equations or polynomials of any order. The system estimates the dynamic component of a drifting process or system and thereby identifies the trend of output response variables of the controlled process. Using this information, the system predicts future outputs based on a history of past and present inputs and outputs, thereby recommending the necessary control action or recipe (set of input parameters) to cancel out the drifting trend. A specific embodiment is a system for the adaptive control of photoresist thickness, uniformity, and dispense volume in the spin coating of wafers in integrated circuit manufacturing. Methods used in the adaptive control system are adaptable to control many processes not readily modeled by physical equations.