2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8478Recent years have seen major advances in understanding the state of the intergalactic medium (IGM) at high redshift. Some aspects of this understanding are reviewed here. In particular, we discuss: (1) Different probes of IGM like Gunn-Peterson test, CMBR anisotropies, and neutral hydrogen emission from reionization, and (2) some models of reionization of the universe.20 pages, 8 figures, Invited article; to appear in Current Science (special section on Cosmology)Astrophysicstext