Plasma polymerized layers are important for many different industrial applications and technologies. This includes also high tech applications in sensor technologies and life science where functionalized surfaces are required. The problem is up to now the mechanism of plasma polymerization is poorly understood. The relationship of polymerization to fragmentation and polyrecombination reactions is not known as well as the contribution of these reactions to the formation of the polymer layer is not clear. This book focus on the investigation of the surface functionalization and volume properties of thin plasma deposited films by a combination of dielectric relaxation spectroscopy, XPS, DSC and FTIR. The properties of the films were studied in dependence on the duty cycle. The results were quantitatively analyzed and correlated to each other in detail.