2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/6925Within the context of hierarchical scenarios of gravitational structure formation we describe how an evolving hierarchy of voids evolves on the basis of {\em two} processes, the {\em void-in-void} process and the {\it void-in-cloud} process. The related analytical formulation in terms of a {\it two-barrier} excursion problem leads to a self-similarly evolving peaked void size distribution.Contribution to ``Multi-Wavelength Cosmology'', conference Mykonos, Greece, June 2003, eds. M. Plionis et al. 4 pages, 3 figsAstrophysicstext