This is an interdisciplinary course, to be accessible to students in various fields (condensed matter, complex systems, elementary particles, gravitation and cosmology) with an interest in renormalization. Broadly speaking, renormalisation can be defined, following Wilson’s ideas, as the dependence of the parameters of a physical theory on the scale of the degrees of freedom being described. In most situations, short distance (high energy) degrees of freedom decouple from long distance (low energy ones) but this fails to the case in two situations : high energy virtual particles and fluctuations of the order parameter close to a critical point in a second order phase transition. The latter case, that is easily understandable with only a basic knowledge of thermodynamics and statistical physics, is used to illustrate Wilson’s ideas on renormalisation. Then, the core of the course is to develop similar concepts in the case of quantum field theory and study perturbative renormalisation in the context of Feynman graphs expansions and effective field theories. The aim of the course is to derive some general asymptotic behavior and identify the relevant parameters that govern long distance (low energy) physics. No prior knowledge of relativistic quantum field theory is required since the different notions are presented in the framework of Feynman’s functional integral. More specific examples of applications, either in high energy or statistical physics, are studied through a homework whose topic can be chosen by the students according to their particular project.