2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/44556The lectures are a practical introduction to perturbative calculations in QED and QCD. I discuss methods of calculation of one- and two-loop diagrams in dimensional regularization, MSbar and on-shell renormalization schemes, decoupling of heavy-particle loops.LaTeX2e, 103 pages, 62 figures. The complete paper is also available at http://www-ttp.physik.uni-karlsruhe.de/Preprints/High Energy Physics - Phenomenologytext