Nanometer scale physics is progressing rapidly: the top-down approach of semiconductor technology will soon encounter the scale of the bottom-up approaches of supramolecular chemistry and spatially localized excitations in ionic crystals. Advances in this area have already led to applications in optoelectronics. More may be expected. This book deals with the role of structure confinement in the spectroscopic characteristics of physical systems. It examines the fabrication, measurement and understanding of the relevant structures. It reports progress in the theory and in experimental techniques, starting with the consideration of fundamental principles and leading to the frontiers of research. The subjects dealt with include such spatially resolved structures as quantum wells, quantum wires, quantum dots, and luminescence, in both theoretical and practical terms.