The physics of atomic and molecular clusters is interesting from many points of view. These systems bridge the domains of atomic and molecular physics on one side and condensed matter physics on the other. Their properties may be dominated by their large surface-to-volume ratio, giving a unique opportunity to study the interplay between surface and volume effects. They may exhibit a discrete spectroscopy because of their finite size. A major thrust in the development of high-tech materials can be described as atomic-scale engineering. In this process, materials are assembled on an almost atom by atom basis in order to obtain useful properties not found in naturally-occurring substances.