2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53517Talk given at the ``4th Hellenic School on Elementary Particle Physics", Corfu, 2-20 September 1992: The propagation of strings in cosmological space-time backgrounds is reviewed. We show the relation of a special class of cosmological backgrounds to exact conformal field theory. Particular emphasis is put on the singularity structure of the cosmological space-time and on the discrete duality symmetries of the string background.19 pages + 1 figure, CERN-TH.6850/93High Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext