Thin Metallic multilayer films have become an important part in today's computer technology. The giant magnetoresistance (GMR) effect, which plays a central role here, was discovered in the late 1980s. This can be essentially described as the effect of a magnetic field on the electron transport leading to significant changes in the resistance. Other aspects of multilayers systems, such as stability, growth, confinement are also addressed. Theoretical and experimental methods used in such work are described in some detail, with special emphasis on density functional and spin density functional...