He was a visiting professor for brief periods at many academic institutions, including the University of Bonn in 1989, the University of Paris-Sud in 1997 (and again in 2003 and 2012), MSRI in 2001, the Instituto Nacional de Matemática Pura e Aplicada (IMPA) in 2002 (and again in 2010), the Institute for Advanced Study in 2004, the Institute Henri Poincaré in 2009, the Autonomous University of Madrid in 2011, the University of the Basque Country in 2015, and IHES in 2016.
