2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/49560I review the most important objectives of the physics program of a next-generation e+e- linear collider. (Introductory theory lecture presented at the 1999 International Workshop on Linear Colliders, Sitges, Barcelona, Spain.)19 pages, 5 figures, 2 tables, LaTeXHigh Energy Physics - Phenomenologytext