2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54347Some of the properties of string theory defined on world-sheets with boundaries are reviewed. Particular emphasis is put on the possibility of identifying string configurations (\lq D-instantons' and \lq D-branes') that give rise to stringy non-perturbative effects.Talk presented at the Strings '95 Conference, USC (March 1995). Latex, 10 pagesHigh Energy Physics - Theorytext