2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/39448Anomalous U(1) gauge symmetries appear frequently both in heterotic and type I/type II string theory. In the heterotic case we find at most a single anomalous U(1), while in open string theories several such symmetries can appear. We review the properties of the anomalous gauge bosons, the appearance of Fayet-Iliopoulos terms and the concept of heterotic-type I duality. Phenomenological applications of these symmetries might be different in the type I/type II case compared to the heterotic one.7 pages, Latex, Contribution to the Proceedings of COSMO-99, International Workshop on Particle Physics and the Early Universe, TriesteHigh Energy Physics - Phenomenologytext