Pascal Roussel is Research Director at CNRS in the field of both solid-state chemistry and crystallography. After a Ph.D. at Lab. CRISMAT (Pr Bernard Raveau), Caen, France, and a post-doctoral position at the “Institute of Crystallography” of the University of Aachen, Germany (Pr Gernot Heger), he was hired as CNRS Research scientist at Catalysis and Solid State Chemistry Unit. He defended his Habilitation in 2008 on the subject “Order-disorder phenomena in solids: on the use of X-rays and neutron diffractions” at the University of Lille, France (Pr Francis Abraham) and in 2012 he was promoted as Research Director. His main research areas are the structural studies by mean of X-rays, neutrons, and/or electrons diffraction, the Anharmonicity, the Maximum Entropy Method, the order–disorder in structures, the twinned structures, pseudo-symmetry, etc. and his current research projects are dealing with oxide ionic conductivity in solids, new mixed valence transition metal oxides compounds and new applications. He his since 2014 at the head of the solid state chemistry department of UCCS (around 45 permanent people and 30 non-permanent).