 A century ago economists talked of their work in terms of “principles,” “laws,”, and “theories.” That language has not disappeared altogether: economists still talk of “game theory”, “consumer choice theory”, or the “law of demand”. But nowadays the standard intellectual tool or form in economics is a “model.” Econometricians speak of models and structures. Economists are more comfortable describing the axioms concerning rational choice as constituting a model of rational choice than as delineating a theory of rational choice. Many of the most distinguished commentators on models regard them as fictional worlds, whose study informs our understanding of actual phenomena (Frigg, 2010). “Creating models is ‘world-making.’” (Morgan 2012, pp. 95, 405). In their view, economists are able to investigate how causal factors would operate in the absence of interferences by constructing models —that is fictional economies—in which the interferences are absent. Uskali Mäki maintains that “Models are experiments. Experiments are models.” (2005). Dani Rodrik (2015) argues that economics consists of a collection of models, and that doing economics consists in selecting or customizing a model from this collection. Is the ubiquity of talk of models just a change in terminological fashion, or does the concern with models (which is by no means unique to economics) signal a methodological shift? What are models? These questions have been discussed by Cartwright 1989, 1999, Godfrey Smith 2006, Grüne-Yanoff 2009, Hausman 1992, 2015a, Kuorikoski and Lehtinen 2009, Mäki, ed. 1991, Mäki 2005, 2009a, 2009b, Morgan 2001, 2004, 2012, Morgan and Morrison 1999, Rappaport 1998, Sugden 2000, 2009, Weisberg 2007, and Lehtinen, Kuorikoski and Ylikoski 2012.