This paper addresses what is unquestionably the most important unsolved problem in process control : how to quantitatively incorporate dynamic controllability into conventional steady-state economic design. Historically, plant design was the precursor to control system design. In recent years it has finally been widely recognized that much can be gained by simultaneously designing the plant with its control structure. Reduced capital costs, improved process dynamics, and tighter product specifications are advantages of this approach. This paper outlines a generic methodology called the capacity-based economic approach that can be used to compare or screen preliminary plant designs by quantifying both steady-state economics and dynamic controllability. The method provides an analysis tool that explicitly considers variability in product quality. The design of a simple coupled reactor/stripper system is used to demonstrate the method.