This classic volume, reprinted twenty years after it was first published, takes a close look at the theory of direct nuclear reactions. It emphasizes the microscopic aspects of these reactions and their description in terms of the changes induced in the motion of individual nucleons, except where collective motion in nuclei gives a more succinct description. Assuming only a modest knowledge of quantum mechanics and some acquaintance with angular momentum algebra, the book begins essentially at the beginning. Its goal is to provide the novice with the means of becoming competent to do research on direct reactions, and the experienced researcher with a detailed discussion of advanced topics. For completeness, appendices on angular momentum algebra and special functions are included.