2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/7788I briefly present some current theoretical motivations for time or space variations of the fundamental constants of nature and review current key observational results. I focus on the fine-structure constant, and particularly on measurements using quasars and the cosmic microwave background. I also compare various observational results to the simplest model-building expectations.8 pages, review talk at the XXXIX Rencontres de Moriond (La Thuile, March 2004), to appear in the proceedingsAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext