2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/76215This encyclopedia article briefly reviews without proofs some of the main results in cotangent bundle reduction. The article recalls most the necessary prerequisites to understand the main results.11 pages. To appear in the Encyclopedia of Mathematical Physics. Jean-Pierre Françoise, Greg Naber, Sheung Tsun Tsou (editors). ElsevierSymplectic GeometryDifferential Geometry37Jxx, 53Dxx, 53D20, 70Hxxtext