This project has a long and varied history, both intellectually and geo-graphically. Our interest in models arose in the context of independent work done by Morrison in the history and philosophy of physics and by Morgan in the historical and philosophical aspects of econometrics. Our first conversation about models occurred at the History of Science meeting in Seattle in Fall 1990 and lively discussions comparing modelling in our two fields continued through the early 1990s. Thereafter, from 1993–1996, through the generous support of Nancy Cartwright and the Centre for the Philosophy of the Natural and the Social Sciences (CPNSS) at the London School of Economics, we organised a working research group focusing on issues relevant to modelling in physics and economics. The goal of the project was not to find or construct general principles that these two disciplines shared; instead, our initial focus was empirical – to examine the ways in which modelling works in each field and then move on to investigate how the presuppositions behind those practices influenced the way working scientists looked on models as a source of knowledge. The project at the LSE was directed by Cartwright, Morgan and Morrison and consisted of a group of graduate students who attended regularly, as well as a constant stream of European and American visitors and faculty from various LSE departments such as economics, statistics and philosophy. The CPNSS not only provided support for graduate students working on the project but enabled us to organise seminars and workshop meetings on the topic of modelling.