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 theories.Magnetic anisotropy in thin films is also discussed in this work, while addressing unresolved issues and new results from exchange-bias experiments. This work discusses: the GMR effect; what makes multilayers interesting and useful; and, what are the latest discoveries in this field. It offers: simple insights in to the physics behind multilayers; novel concepts at small length scales; and, theoretical and experimental background.