2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/198245The aim of this set of lectures is a systematic presentation of a 1+3 covariant approach to studying the geometry, dynamics, and observational properties of relativistic cosmological models. In giving (i) the basic 1+3 covariant relations for a cosmological fluid, the present lectures cover some of the same ground as a previous set of Cargèse lectures \cite{ell73}, but they then go on to give (ii) the full set of corresponding tetrad equations, (iii) a classification of cosmological models with exact symmetries, (iv) a brief discussion of some of the most useful exact models and their observational properties, and (v) an introduction to the gauge-invariant and 1+3 covariant perturbation theory of almost-Friedmann-Lema\^ıtre-Robertson-Walker universes, with a fluid description for the matter and a kinetic theory description of the radiation.87 pages. Fully hyperlinked. Published in proceedings of the NATO Advanced Study Institute on Theoretical and Observational Cosmology, Cargèse, France, August 17-29, 1998 / edited by Marc Lachièze-Rey. Boston: Kluwer Academic, 1999. NATO science series. Series C, Mathematical and physical sciences, vol. 541, p.1-116General Relativity and Quantum Cosmologytext