2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34014We give a Hamiltonian definition of mass for spacelike hypersurfaces in space-times with metrics which are asymptotic to the anti-de Sitter one, or to a class of generalizations thereof. We show that our definition provides a geometric invariant for a spacelike hypersurface embedded in a space-time.49 pages, Latex2e with several style files; minor misprints corrected here and thereGeneral Relativity and Quantum Cosmologytext