This volume contains a partial collection of lectures delivered at the workshop on "Nuclear Reaction Data and Nuclear Reactors: Physics, Design and Safety", held at the Abdus Salam International Centre for Theoretical Physics in February-March 2002. The aim of the Workshop was to present extensive, and up-to-date information on the whole scientific field underlying nuclear reactor calculations, from the theory of nuclear reactions and nuclear data production and validation down to the applications to nuclear reactor physics, design and safety. In particular, the collection of lecture notes included in this volume presents techniques for modelling microscopic calculations of light nuclei reactions, the use of a database of parameters for calculations of nuclear reactions and the nuclear data requirements for the calculation of the decay heat in nuclear reactors. As far as the nuclear reactors themselves are concerned, the elds of advanced nuclear technology developments for power production, of non-electric applications of nuclear energy and of the safety procedures for decommissioning old nuclear power plants are covered. We hope that, although limited to these few topics, the volume will nevertheless represent a useful reference for researchers interested in the field of nuclear data and nuclear reactors. For the benefit of potential readers who could not participate in the Workshop, these lecture notes are also available on-line at: http://www.ictp.it/pub_off/lectures/ for free access and consultation. (ISBN 92-95003-30-6)