Thin-film knowledge and nanometer-structure technology play a crucial role in the high-tech industries. Whilst the major exploitation of thin films has been in microelectronics, there are numerous applications in communications, optical electronics, coatings of all kind, and in energy generation and conservation strategies. The roadmap of the semiconductor industry brings about the strongest need to the production and understanding of thin-films, small structures and semiconductor-metal junctions. Not only the formation and generating of nanometer structures are known to be quite intricate, but also the electron behavior in such solids with limited extensions. Besides theoretical description of electrons in a bulk and at surfaces of metals and semiconductors, the interaction of light with a medium and the classical dispersion theory are shown here. It follows then the concept of plasmons and the 3d-Fermi-liquid theory, which is briefly sketched and widely applied to electron-electron interaction in 2d and smaller structures. This book is useful for researchers, engineers and practitioners in science and industry, as well as for everyone, interested in nanotechnology.