2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/10363I review the theory of hierarchical clustering, starting with an historical overview and moving on to a discussion of those aspects of dissipationless clustering under gravity which are most relevant to galaxy formation. I conclude with some comments on the additional problems which arise when including all the other physics needed to build a realistic picture for the origin and evolution of the galaxy population.Position paper for the 78th Dahlem Conference: The Evolution of the UniverseAstrophysicstext