2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/56157A review is given of the status and developments of the research program aiming to reformulate the physics of the four interactions at the classical level in a unified way in terms of Dirac-Bergmann observables with special emphasis on the open mathematical, physical and interpretational problems.40 pages, revtex file, Invited contribution to the book of the Indian National Science Academy for the International Mathematics Year 2000 adHigh Energy Physics - TheoryAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Phenomenologytext