Michel Callon is Professor at the Ecole des Mines de Paris, and a researcher at the Centre de Sociologie de l?Innovation. Together with Bruno Latour and John Law he was one of the early developers of actor-network theory. He works on the anthropology of markets and the study of technical democracy, and is completing research on French patients? organizations with Vololona Rabeharisoa. His recent books include Le pouvoir des malades (Presse de l?Ecole des Mines, 1999, with V. Rabeharisoa) and Agir dans un monde incertain (Seuil, 2001, with P. Lascoumes and Y. Barthe). In 2002, the Society for Social Studies of Science awarded him the Bernal Prize. Yuval Millo is lecturer in the Department of Accounting at the London School of Economics and Political Science. Having background in the sociology of science and economic sociology, Yuval Millo applies qualitative approaches combined with social networks analysis in the study of financial risk management and corporate governance. Among his latest publications are ?Negotiating a Market, Performing Theory: The Historical Sociology of a Financial Derivatives Exchange? (American Journal of Sociology, 2003, with Donald MacKenzie), ?From Risks to Second-order Dangers in Financial Markets: Unintended Consequences of Risk Management Systems? (New Political Economy, 2005, with Boris Holzer), and ?Regulatory Experiments: Genetically Modified Crops and Financial Derivatives on Trial? (Science and Public Policy, 2006, with J. Lezaun). Fabian Muniesa is a researcher at the Centre de Sociologie de l?Innovation, within the Ecole des Mines de Paris. His work primarily aims at analysing the role of technical instruments in the shaping of markets and at contributing to an empirical, pragmatist approach to the study of calculation. He is the author of several articles and book chapters on the social studies of finance. His main research topics in this area are trading technologies and the automation of financial markets. He is also the co-editor (with D. MacKenzie and L. Siu) of Do Economists Make Markets? On the Performativity of Economics (Princeton University Press, 2007). His current research interests include economic experiments, public management and the sociology of architecture.