NATO ASI Series E: Applied Science This book describes the state of the art on the luminescent properties of porous silicon. The dramatic results of the major international laboratories and groups working in this subject are presented. The majority of the participants agree that a quantum confinement effect and a good passivation of the surface crystallites are responsible for the observed luminescence properties. New characterisation techniques are for the first time presented as a comprehensive survey of the theoretical models. Both efficient and wavelength tunable electroluminescence are demonstrated using liquid contacts and a cathodic injection system. Localised cathodoluminescence in a scanning electron miscroscope and a scanning tunneling microscope is also presented. This book demonstrates that a consensus is emerging on the origin of the visible luminescence of highly porous Si. This novel nanostructure is extending our knowledge into a new area of solid state physics