2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46339Theoretical ideas related to the existence of glueballs in QCD are reviewed. These include non-perturbative phenomena such as confinement, instantons, vacuum condensates and renormalons. We also discuss glueball dominance of the trace of the stress-tensor, the mass content of the nucleon and a theorem on the lightest glueball state.14 pages. Talk given at the Montpelier Conference and Paris Workshop on QCDHigh Energy Physics - Phenomenologytext