In a detailed reconstruction of the genesis of Feynman diagrams the author reveals that their development was constantly driven by the attempt to resolve fundamental problems concerning the uninterpretable infinities that arose in quantum as well as classical theories of electrodynamic phenomena. Accordingly, as a comparison with the graphical representations that were in use before Feynman diagrams shows, the resulting theory of quantum electrodynamics, featuring Feynman diagrams, differed significantly from earlier versions of the theory in the way in which the relevant phenomena were conceptualized and modelled. The author traces the development of Feynman diagrams from Feynman's struggle with the Dirac equation in unpublished manuscripts to the two of Freeman Dyson's publications which put Feynman diagrams into a field theoretic context. The author brings to the fore that Feynman and Dyson not only created a powerful computational device but, above all, a new conceptual framework in which the uninterpretable infinities that had arisen in the old form of the theory could be precisely identified and subsequently removed in a justifiable manner.