Marc Mezard is a professor at Univ. Paris-Sud, and has worked for close to 30 years on the statistical physics of disordered systems. Disorder arises since the constituents can be different from each other (spins, neurons, hard/soft regions in a material) or since they see different environments. An example of this is given by glasses, where the particles freeze in random-looking positions and the geometry of the arrangement is far from a crystal. Mezard has been one of the main forces behind this field, which extends from condensed matter physics to statistical mechanics, and moreover has found applications in many areas outside of physics: computer science (combinatorial optimization, error correcting codes), neural networks, structural glasses, or models of complexity in economics.