The gravity-gauge theory correspondence

At the end of 1997 a young Argentinian physicist conjectured that certain string theories are identical to certain other well-understood theories called gauge theories. This conjecture has been at the focus of attention of much of the string theory community over the last year and a half, and has generated over 1000 research papers. In this article an attempt is made to explain the conjecture and why it has generated so much excitement. (author)