Part I. The What, Why, and How of Economic Ontology: 1. Economic ontology: What? Why? How? Uskali Mäki; 2. The empirical presuppositions of metaphysical explanations Harold Kincaid; 3. Quality and quantity in economics: the metaphysical construction of the economic realm; Part II. Rationality and Homo Economicus: 4. The normatic core of rational choice Russel Hardin; 5. The virtual reality of homo economicus Philip Pettit; 6. Expressive rationality: is self worth just another kind of preference? Shaun Hargreaves; 7. Agent identity in economics John Davis; 8. Chances and choices: notes on probability and beliefs in economic theory Jochen Runde; Part III. Micro, Macro, and Markets: 9. Essences and markets John O'Neill; 10. The metaphysics of microeconomics Alex Rosenberg; 11. Ontological commitments of evolutionary economics Jack Vronen; 12. Is macroeconomics for real? Kevin D. Hoover; 13. The possibility of economic objectivity Don Ross and Fred Bennet; Part IV. The World of Economic Causes: 14. Ceteris paribus laws and socio-economic machines Nancy Cartwright; 15. Tendencies, laws, and the composition of economic causes; 16. Economics without mechanism John Dupre; Part V. Methodological Implications of Economic Ontology: 17. Sargent's symmetry saga: ontological versus technical constraints; 18. Two models of idealization in economics Alan Nelson; 19. The way the world works (www): towards an ontology of theory choice Uskali Mäki.