The evolution of process modeling is traced starting with bipolar technology in the 1960's through recent processing concerns for oxide-isolated MOS devices. The kinetics of diffusion and oxidation are used to illustrate both physical and numerical effects. The interaction of device effects with process modeling is discussed as well as the statistical implications of process variables. The nature of computer-aided design tools for process and device modeling are discussed. This includes tools that bridge gaps between technology and system design with potential application for manufacturing.