A new formulation is presented for the optimal design of multipurpose plants. The proposed model permits a detailed consideration of the design problem taking account of trade-offs between capital costs, revenues and operational flexibility. The optimal solution involves the selection of the required processing and storage equipment items, and the required levels of provision of other production resources such as utilities, manpower, cleaning and transportation equipment. The recently proposed unified Resource-Task Network (RTN) framework (Pantelides, 1994) is used for the process representation. A simple Mixed Integer Linear Programming (MILP) formulation is developed. Binary variables are used to represent the operational and structural choices that have to be made. An example illustrating the flexibility and the applicability of the new approach to the design of multipurpose batch plants is presented.