Pierre Cartier is a member of the IHES, alumnus of the Ecole Normale Supérieure and former research director at CNRS. A long associate of the Bourbaki group, he is known for his wide range of interests and contributions, among others in algebraic geometry, representation theory and mathematical physics. He is one of the founders of the theory of coalgebras and Hopf algebras.Frédéric Patras, alumnus of the Ecole Normale Supérieure and research director at CNRS, is an expert in the theory of Hopf algebras and their applications in analysis, combinatorics, Lie theory, probability, theoretical chemistry and physics. He has published and edited over a hundred works on various subjects.