Ernst Stueckelberg's and Nikolay Bogoliubov's work on the causal perturbation theory approach in the early 1950s is not widely known, yet it made conceptual moves that remain relevant to the foundations of QFT. I will discuss two issues illuminated by this early work in the causal perturbation theory programme. i) In using a causality condition rather than a dynamical equation to set up the perturbation series Stueckelberg and Bogoliubov pioneered the idea that perturbative QFT is distinct from, and can be developed independently of, an 'exact' non-perturbative characterization of QFT. ii) This approach led to a reconceptualization of the perturbative renormalization procedure, understanding it in terms of the fixing of ambiguities flowing from the causality condition rather than a subtraction of divergences. This view of renormalization formed the basis of Stueckelberg and Petermann's (1953) introduction of the renormalization group, thus the causal perturbation theory programme served as an incubator for ideas in renormalization theory which would become much more prominent and important in later decades.Foundations of Quantum Field Theory: 2019 Annual Philosophy of Physics ConferenceJune 12 - 14, 2019James Fraser,?EUR< Durham UniversityVisit the Rotman website for more information on applications, events, project descriptions, and openings. http://www.rotman.uwo.caFollow The Rotman Institute on Twitter: https://twitter.com/rotmanphiloLike The Rotman Institute on Facebook: https://www.facebook.com/rotmanphilos...Subscribe to our channel: https://www.youtube.com/user/rotmanph...