2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8138In an introductory manner, the nature of dark energy is addressed, how it is observed and what further tests are needed to reconstruct its properties. Several theoretical approaches to dark energy will be discussed.Keynote talk to joint session of 5th Rencontres du Vietnam, Hanoi.August 2004. 6 pages. Minor corectionsAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - PhenomenologyHigh Energy Physics - Theorytext