Grossmann, I.E.Halemane, K.P.Swaney, R.E.The objective of this paper is to give an overview of the optimization strategies that are required when designing chemical processes in which the existence of regions of feasible steady- state operation must be ensured in the face of parameter variations. Two major areas are considered: optimal design with a fixed degree of flexibility, and design with optimal degree of flexibility. For the first area the problems of multiperiod design, and design under uncertainty are analyzed. For the second area the problem of deriving an index of flexibility in the context of multiobjective optimization is discussed. As shown in the paper, the major challenge in these problems lies in the development of efficient solution procedures for large scale nonlinear programs which are either highly structured, or otherwise involve an infinite number of constraints.en-USTechnical Report