A conversation with S. R. S. Varadhan

S. R. S. Varadhan was awarded the Abel Prize for the year 2007. I met him on 14 and 15 May-one week before the prize ceremony in Oslo-in his office at the Courant Institute to interview him for the Mathematical Intelligencer. My qualifications to interview him were that he and I are Ph.D.'s from the same institute, my Varadhan number is 2, and his was the first research talk that I attended as a graduate student My major disqualification was that I know little of probability, and I felt like someone destitute of geometry daring to enter Plato's Academy. Though we had planned to talk for two or three hours, our conversation was spread over nearly eight hours. What follows is the record of this with very minor editing. To help the reader I have added a few "box items" that explain some of the mathematical ideas alluded to in the conversation.