2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/132549In this talk I gave a brief summary of leading order, next-to-leading order and shower calculations. I discussed the main ideas and approximations of the shower algorithms and the related matching schemes. I tried to focus on QCD issues and open questions instead of making a inventory of the existing programs.Plenary talk at 15th International Workshop on Deep Inelastic Scattering and Related Subjects (DIS 2007), Munich, Germany, 16-20 Apr 2007. 12 pages, 9 figures; added referencesHigh Energy Physics - Phenomenologytext