Lionel Salem (born 1937) is a French theoretical chemist, known for his fundamental contributions to quantum chemistry and organic reaction mechanisms. During his career, he was a Director of Research at the CNRS and a professor at the University of Paris-Sud in Orsay. His research focused on the interaction of molecular orbitals to explain chemical reactivity, particularly in pericyclic reactions, providing important theoretical foundations for organic chemistry. He is the author of influential works, including the academic text "The Molecular Orbital Theory of Conjugated Systems" and popular science books such as "La Molécule, la merveilleuse" and "La plus belle histoire de la molécule". He has also written novels, exploring the intersection of science and creativity. For his work, he has received numerous awards, including the Prix du Rayonnement Français for chemistry, and is a member of the International Academy of Quantum Molecular Science.