The Resource-Task Network process representation provides a conceptually simple, unified framework for the development of mathematical programming formulations for multipurpose plant scheduling and design. However, the consideration of complex production processes sometimes leads to very large RTNs and, consequently, mixed integer optimisation problems that are difficult or impossible to solve using currently available techniques. One way of reducing the sim of the RTN representation of a process is to identify functional equivalences among subsets of the available resources, thereby allowing a more aggregate treatment of these resources. This paper provides the necessary theoretical-basis for the exploitation of partial resource equivalence, which allows large RTNs to be reduced to smaller but completely equivalent ones. Such reductions are particularly significant in problems involving many sequence-dependent changeovers. Examples illustrating these ideas and their impact are presented.