2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/149162I discuss some current thoughts on how low-energy measurements and consistency constrain theories at high energies with emphasis on string theory. I also discuss some recent work on the dynamics of supersymmetric gauge theories.14 pages, latex, world_sci.sty, no figures, minor typos correctedHigh Energy Physics - TheoryHigh Energy Physics - Phenomenologytext