This chapter considers the framework needed in order for mathematical and physical structures to be examined and related, in philosophical terms. We contrast the structuralist account associated with Joseph Sneed, Wolfgang Stegmüller, and others with the models-focused account of Ron Giere. The former, we claim, is heavy on formalism at the expense of a consideration of practice, whereas the latter draws on a number of case studies but omits the crucial formal framework. We suggest rejecting both these extremes in favour of an approach that is appropriately formal, while retaining the ability to represent science as actually practised. We maintain the partial structures account we present here constitutes such an approach. In particular, this framework can accommodate the heuristic role of surplus mathematical structure, as described by Michael Redhead. The exploitation of such structure is a crucial feature of scientific practice that we return to throughout the book.