Summary form only given. About two years ago Bourgain, Katz and Tao (2004) proved the following theorem, essentially stating that in every finite field, a set which does not grow much when we add all pairs of elements, and when we multiply all pairs of elements, must be very close to a subfield. Theorem 1: (Bourgain et al., 2004) For every /spl epsi/ > 0 there exists a /spl delta/ > 0 such that the following holds. Let F be any field with no subfield of size /spl ges/ |F|/sup /spl epsi//. For every set A /spl sube/ F, with |F|/sup /spl epsi// |A|/sup 1 + /spl delta// or the product set |A /spl times/ A| > |A|/sup 1 + /spl delta//. This theorem revealed its fundamental nature quickly. Shortly afterwards it has found many diverse applications, including in number theory, group theory, combinatorial geometry, and the explicit construction of extractors and Ramsey graphs, mostly described in the references below. In my talk I plan to explain some of the applications, as well as to sketch the main ideas of the proof of the sum-product theorem.