2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/54012The Kaluza-Klein idea of extra spacetime dimensions continues to pervade current attempts to unify the fundamental forces, but in ways somewhat different from that originally envisaged. We present a modern perspective on the role of internal dimensions in physics, focussing in particular on superstring theory. A novel result is the interpretation of Kaluza-Klein string states as extreme black holes.(Talk delivered at the Oskar Klein Centenary Nobel Symposium, Stockholm, September 19-21, 1994.)38 pages latex, NI-94-015High Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext