This book, devoted to the study of quantum effects in atomic systems, reviews the state of the art in the fields of Bose--Einstein condensation, quantum information processing, and the problems of propagation of matter waves in complex media. The specific topics include: theory and experiments in Bose--Einstein condensation, theory and experiments on decoherence phenomena in simple quantum systems and the connection to quantum measurement, atom interferometry, quantum computing, multiple scattering problems in atomic physics, quantum and nonlinear optics in a photonic band gap and quantum chaos and atomic physics. Pedagogical in style, the articles address PhD students as well as researchers.