"Duality, Spacetime, and Quantum Mechanics," by Edward Witten. Physics Today, May 1997, pages 28-33.
This article discusses some of the major themes and ideas that coalesced into what Witten calls "the second superstring revolution," which occurred in 1994-1995. String theory is a theory of matter in which elementary particles are modeled as vibrating strings. The article ranges over classical ideas, such as the duality between electric and magnetic fields, to cutting edge topics like supersymmetry. One of the main ingredients in this discussion is four-dimensional quantum gauge theories, the investigation of which forms an active topic of current research. According to the article, the second superstring revolution has developed "a major new perspective on the quest for superunification of the forces of nature."
--- Allyn Jackson