This is part of the very successful series in Advances in Chemical Physics by the same editor as Dynamics of the Excited State. It follows the same format as other volumes, as a specialist volume with a range of articles which are designed to cover the whole field, giving a balanced picture. The contents cover both theoretical and practical aspects of the subject matter named in the title. A complete survey of the field is aimed at, ranging from laser isotope separation at the applied end to current theories of the quantum mechanics of photodissociation.