2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/44859We review recent work on the strong CP problem in the context of realistic string-inspired models. We discuss the various solutions, review the conjecture that CP is generally a gauged discrete symmetry in string theory and then consider models of the Nelson-Barr type. We note that squark non-degeneracy spoils the Nelson-Barr structure at the one loop level. We stress that string theory expectations, as well as naturalness arguments, make it very difficult to avoid the constraints on non-degeneracy.preprint SCIPP 93/14; 10 pages, latex format, uses epsf.tex for 2 figures, submitted separately via `uufiles'High Energy Physics - Phenomenologytext