Center for Game Theory in Economics: Home Page of the Center for Game Theory in Economics, SUNY at Stony Brook.
Center For Rationality and Interactive Decision Theory: Research on game theory, decision theory, rationality and related topics at the Hebrew University of Jerusalem
Econometric Society: International society dedicated to advancing research in theoretical and quantitative economics.
Game Theory and Mathematical Economics: Institute of Mathematics, Wroclaw University of Technology, Poland.
Institute of Economic Theory I, Humboldt University: Research mainly on auction theory, mechanism design, industrial organization and applied game theory directed by Prof. Wolfstetter, Berlin
Institute of Economic Theory III, Humboldt University: Research on game theory and experimental economics directed by Prof. Gueth, Berlin
Institute of Mathematical Economics, University of Bielefeld: Research focusing also on game theory (Prof. Rosenmueller, Prof. Trockel)
International Society of Dynamic Games: Promotes interactions among researchers. Publishes an archival journal, Annals of Dynamic Games.
International Society of Dynamic Games, Russian Chapter: Center of Game Theory, Faculty of Applied Mathematics and Control Processes, Saint-Petersburg State University.
Seville Game Theory Group: Lots of links on game theory, papers and publications by members and others.
The ESRC Centre for Economic Learning and Social Evolution: Research on learning theory, experimental economics and evolutionary game theory at University College, London (Binmore and others)