Molecular hydrogen is the most abundant molecule in the Universe. In recent years, advances in theory and laboratory experiments coupled with breakthrough observations with important new telescopes and satellites have revolutionized our understanding of molecular hydrogen in space. It is now possible to address the question of how molecular hydrogen formed in the early Universe and the role it played in the formation of primordial structures. This volume presents articles from a host of experts who reviewed this new understanding at an international conference in Paris. It covers the theory of the physical processes and laboratory experiments, as well as the latest observations. It will be an invaluable reference for all students and researchers in astrophysics and cosmology.