2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/53139Prepared for the Quantum Field Theory section of the Encyclopedia of Mathematical Physics, Elsevier, 2006. A brief introduction to the methodology and techniques of perturbative relativistic quantum field theory is presented.18 pages, 9 figures; v2: typos corrected; Contribution to the Encyclopedia of Mathematical Physics, Elsevier, 2006High Energy Physics - TheoryHigh Energy Physics - Phenomenologytext