This volume is a celebration of the state of mathematics at the end of the millennium. Produced under the auspices of the International Mathematical Union (IMU), the book was born as part of the activities of World Mathematical Year 2000. It consists of 28 articles written by influential mathematicians. Authors of 14 contributions were recognized in various years by the IMU as recipients of the Fields Medal, from K.F. Roth (Fields Medalist, 1958) to W.T. Gowers (Fields Medalist, 1998).
