Harvard University, Fall semester, 1982
University of Pennsylvania, Winter 1983
Stanford University, Spring quarter, 1983
Visiting Fellow, University of California, Berkeley, Math Sciences Research Institute, January-March, 1986
Fellow Commoner, Churchill College, Cambridge, Cambridge University, April-June, 1986 and May-June 1987
École Polytechnique, Paris, July-August 1986
Stanford University, IMSSS, July-August 1987
Indira Gandhi Institute of Economic Development, Bombay, India, December 1987
KEPE, Research Institute of Greece, Athens, May 1988
University of Bonn, June 1988
Santa Fe Institute, Santa Fe, New Mexico, June 1989
Stanford University, IMSSS, August 1989
Kidder, Peabody & Co., February-July, 1990
Santa Fe Institute, January-June 1991
CORE, Université Catholique de Louvain, May 24-June 5, 1992
Hebrew University Third Jerusalem Summer School, June 15-24, 1992
Massachusetts Institute of Technology, Spring Semester 1996
Hebrew University, Eighth Jerusalem Summer School, June 16-25, 1997
Columbia University, Spring Semester 2002
Université Paris 1 Panthéon-Sorbonne, Fall 2004
Stanford University, SIEPR, Spring Semester 2011
Hebrew University Twenty-Second Jerusalem Summer School, June 15-24, 2011