2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/50130Superstring theory has continued to develop at a rapid clip in the past few years. Following a quick review of some of the major discoveries prior to 1998, this talk focuses on a few of the more recent developments. The topics I have chosen to present are 1) the use of K-theory to classify conserved charges carried by D-branes; 2) tachyon condensation on unstable D-brane systems; and 3) an introduction to noncommutative field theories and their solitons.13 pages; Talk presented at the Conference Quantization, Gauge Theory, and Strings dedicated to the memory of Professor Efim Fradkin and at the Ninth Marcel Grossmann Meeting (MG9)High Energy Physics - Theorytext