2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/108176I review the essentials of ultrahigh-energy neutrino interactions, show how neutral-current detection and flavor tagging can enhance the scientific potential of neutrino telescopes, and sketch new studies on neutrino encounters with dark matter relics and on gravitational lensing of neutrinos.19 pages, 11 figures in 19 files, uses pdproc.sty (included). Invited talk at NO-VE 2006, Neutrino Oscillations in VeniceAstrophysicsHigh Energy Physics - Phenomenologytext