AbstractAs steady‐state and dynamic simulators with optimal controllers have evolved, tools for nonlinear analysis have been developed by reactor and thermophysical property specialists. Designers lag behind in developing and utilizing these tools, as many design strategies assume idealized behavior even though processes contain an increasing number of nonlinear elements. This article examines the sources of the nonlinear elements, often associated with physical and chemical interactions, in designs and their control systems. Promising methods for nonlinear analysis are reviewed.In each design activity, involving simulation, economic optimization, projections of controllability and operability, emphasis is on the sources of nonlinearities and solution methods. These are examined for the equality constraints and nonlinear programs in phase and chemical equilibria, in reactors and separators, and in the simulation and optimization of flowsheets. Also examined are the impact of non‐linear predictive control in screening designs and methods to insure operability, in the face of uncertaint