2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/55761This is an introduction to some recent developments in string theory and M theory. We try to concentrate on the main physical aspects, and often leave more technical details to the original literature.76 pages, harvmac. v2: A few typos corrected, a reference addedHigh Energy Physics - Theorytext