Delve into the world of computational physics and chemistry with this 2-hour 52-minute lecture from the CECAM-MARVEL Classics series. Learn about fundamental methods in molecular and materials modelling directly from pioneers Antoine Georges and Gabriel Kotliar. Explore topics such as quantum excitations, locality, physical limits, optical conductivity, and the Mean Field Theory tree. Gain insights into efficient impurity solvers, Dynamical Mean Field Theory (DMFT) and electronic structure, and the application of these concepts to transition metal oxides. The lecture concludes with a Q&A session, allowing for deeper understanding of these milestone methods and algorithms. Suitable for master and graduate students, this presentation offers a unique opportunity to learn about the genesis of work now recorded in textbooks, directly from the originators themselves.