 in 1974-76, and has been on the faculty of the University of Toronto since 1977, where he served as Chair during 1987-91.He has also spent several years at the Institute for Advanced Study.In addition to his individual work, he has been notable for his collaborations with other well-known number theorists, including Enrico Bombieri, William Duke, Andrew Granville, and especially Henryk Iwaniec.