is infinitely more ambitious than that: it attempts to provide a complete, unified, and consistent description of the fundamental structure of our universe. (For this reason it is sometimes, quite arrogantly, called a 'Theory of Everything'). The essential idea behind string theory is this: all of the different 'fundamental ' particles of the Standard Model are really just different manifestations of one basic object: a string. How can that be? Well, we would ordinarily picture an electron, for instance, as a point with no internal structure. A point cannot do anything but move. But, if string theory is correct, then under an extremely powerful 'microscope' we would realize that the electron is not really a point, but a tiny loop of string. A string can do something aside from moving--- it can oscillate in different ways. If it oscillates a certain way, then from a distance, unable to tell it is really a string, we see an electron. But if it oscillates some other way, well, then we call it a photon, or a quark, or a ... you get the idea. So, if string theory is correct, the entire world is made of strings! Perhaps the most remarkable thing about string theory is that such a simple idea works--- it is possible to derive (an extension of) the Standard Model (which has been verified experimentally with incredible precision) from a theory of strings. But it should also be said that, to date, there is no direct experimental evidence that string theory itself is the correct description of Nature. This is mostly due to the fact that string theory is still under development. We know bits and pieces of it, but we do not yet see the whole picture, and we are therefore unable to make definite predictions. In recent years many exciting developments have taken place, radically improving our understanding of what the theory is. If you want to learn more, visit the sites listed below. I also highly recommend the popular science book "The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest for The Ultimate Theory" (W. W. Norton & Company, 1999), written by Prof. Brian Greene, a well-established string theorist. * The Official String Theory Website: An excellent introductory site for the nonspecialist, including RealAudio interviews with leading string theorists, and a tour of the Big Bang. * The Elegant Universe: The companion site for the 3 hour PBS series based on Brian Greene's book. You can even watch the series online. (Unfortunately, it is nowhere near as good as the book! It is visually stunning, but the physics content is extremely low and the approach is excessively propagandistic. You can read a critical NY Times review of the series here.) * Particle Adventure: A very nice tour through the main ideas of the Standard Model of particle physics.(Also available in Spanish and other languages). * The Science of Matter, Space and Time: Another nice presentation of the concepts of particle physics. * Einstein's Unfinished Symphony: An article on string theory that appeared recently in TIME magazine, on occasion of TIME's designation of Einstein as the person of the 20th century. * Strings '00 Pictures: Photos of some of the world's leading string theorists, at the most important yearly conference on the subject (see also the ITP M Theory Program and Strings 96 pictures). * Black Holes, Strings and Quantum Gravity: A public lecture by Prof. Juan Maldacena, undoubtedly the most influential string theorist in the last few years (also available in Spanish). * Superstrings! Home Page: A nice site where many aspects of string theory are explained. * Duality, Spacetime and Quantum Mechanics: A public lecture by Prof. Edward Witten (IAS Princeton), arguably the world's most influential theoretical physicist, and a leading contributor to string theory * The Theory of Strings--- A Detailed Introduction: An extensive description of the basic ideas of the theory, by Prof. Sunil Mukhi, a leading string theorist. * String Reviews: List of downloadable review articles on various topics in string theory. Most of them are highly technical, but some of the articles in the "Colloquia/Semipopular" category are intended for a wider audience. * String Theory and the Unification of Forces: An explanation of t