This book is aimed at anyone who has ever wondered how canonical quantization, the LSZ reduction formula, path integrals, Feynman diagrams, and renormalization are interconnected. Written in a casual style, it serves as a companion reading for lectures on quantum field theory or for self-study, providing conversational explanations and calculation tricks that are very helpful for beginners. The first part introduces fundamental concepts from classical field theory to renormalization using scalar fields. The second part generalizes these concepts for fields with spin and lays the groundwork for the third part with the introduction of the gauge principle. Here, applications to the real world are addressed: quantum electrodynamics and its renormalization, as well as the standard model of particle physics and the Higgs mechanism.