2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/113260I review our current knowledge of the mass distribution in clusters, as obtained from the analysis of the projected phase-space distribution of cluster galaxies. I discuss the methods of analysis, their relative advantages and disadvantages, and their reliabilities. I summarize the most recent and important results on the mass distributions of galaxy systems, from nearby to medium-distant systems, and from groups to clusters. In particular I consider how well different proposed models fit the observed cluster mass distribution, and which are the relative distributions of galaxies, baryons, and dark or total mass in clusters. I also discuss the current observational evidence for mass accretion onto galaxy systems, coming mostly from the analysis of the velocity anisotropy profiles.12 pages, 2 figures. Proceedings of the XLIst Rencontres de Moriond, XXVIth Astrophysics Moriond Meeting: "From dark halos to light", Eds. L.Tresse, S. Maurogordato and J. Tran Thanh Van (Editions Frontieres). Invited reviewAstrophysicstext