2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/148622This is a review of the properties of spectral fluctations in disordered metals, their relation with Random Matrix Theory and semiclassical picture. We also review the physics of persistent currents in mesoscopic isolated rings, the parametric correlations and curvature distributions.45 LateX pages, 15 postscript figures, Minor typos have been corrected and references updatedMesoscale and Nanoscale Physicstext