Julien Lesgourgues is an engineer of the Ecole Polytechnique in Paris. He obtained his Ph.D. in 1998 at the University of Tours, France. He is currently a researcher at CERN and the EPFL in Switzerland and CNRS in France. His research is focused on the phenomenology of cosmological models, and more specifically on the observable signatures of dark matter, neutrinos, and cosmological inflation. He is a member of the Planck satellite collaboration.