In this book, a number of the world's leading researchers in quantum, classical and atomic physics cooperate to present an up-to-date account of the recent progress in the field. The first part highlights the latest advances in semiclassical theory, whilst the second one is devoted to applications to atomic systems. The authors present the material in pedagogical form to make it easy reading for non-specialists, too. Among the topics treated, the reader will find a new quasiclassical quantization scheme for Hamiltonian dynamics, an application of the semiclassical formalism to photodissociation of small molecules and to the Lorentz gas and discussions of tunneling corrections. Furthermore, one finds papers on chaotic ionization, on the behaviour of hydrogen atoms in external fields, e.g. magnetic or microwave fields.