2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/45632Two models incorporating different forms of spontaneously broken quark-lepton symmetry are discussed. Both models are constructed so that quark-lepton symmetry can be broken at as low an energy scale as phenomenology allows, thus maximising their testability. The first model uses the Pati-Salam gauge group SU(4)$\otimes$SU(2)$_L\otimes$SU(2)$_R$. The main analysis presented here concerns large threshold corrections to the $m_b = m_τ$ tree-level mass relation. The second model is a new and simplified theory using discrete quark-lepton symmetry which has a very economical Higgs sector and elegantly avoids a potential quark-lepton mass relation problem.6 pages, LaTeX, invited talk at Valencia 95 (to appear in the Proceedings)High Energy Physics - Phenomenologytext