2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49934Anomalous U(1) gauge symmetries can appear both in heterotic and type I string theories. In the heterotic case we find a single anomalous U(1), while in open string theories several such symmetries can appear. Nonetheless, there is a conjectured duality symmetry that might connect these two theories. We review the properties of anomalous gauge symmetries in various string theories as well as the status of this heterotic-type I/II duality. We also comment on the possible phenomenological applications of anomalous gauge symmetries in string theory.7 pages, Latex, JHEP, Contribution to the Proceedings of TMR99, European Program Meeting on Quantum Aspects of Gauge Theories, Supersymmetry and Unification, Paris, September 1999High Energy Physics - Theorytext