Over the last 40 years or so, economics has become a modelling science: a science in which models have become one of the main epistemological tools both for theoretical and applied work. But providing an account of how models work and what they do for the economist is not easy. For the philosopher of economics like me, struggling with this question, John Sutton's views on the nature and design of economic models and how they work is indeed thought provoking. Because of my own interests, my review of Sutton's book: Marshall's Tendencies: What Can Economists Know? will focus on three related issues that I found especially intriguing in his treatment of the role of models in modern economics. The first is the way that Sutton's account fits with my own reading of the history of twentieth-century economics, namely that the focus of economic explanation has moved during the last century from ‘theories’ and ‘laws’ to ‘models’ and ‘mechanisms’. The second is to understand the epistemological connotations of Sutton's ‘class of models’ view. The third is to explore what Sutton means when he says a model ‘works’. These three questions roughly coincide with the material presented in Chapters 1, 3 and 2 respectively of the book. As we shall see, Sutton gives us a practitioner account of applied economics which can fit within the standard terms used by philosophers of economics on theory-testing, but which reveals a number of novel elements for philosophical analysis.