Book excerpt: Layered thin film structures often have unusual properties which make them appealing in a wide range of applications. Fabrication of submicron and nanometer multilayers can produce metastable phases that many not be predicted from the bulk equilibrium phase diagrams. Understanding the growth, structure, stability and properties of multilayers, and controlling their microstructure through processing, are important in many applications. This book focuses on the relationship of structure and processing to the properties that are relevant to all researchers in the field of multilayers. Topics include: phase transformation and reaction kinetics; processing and growth; structural characterization; magnetic, electronic and optical properties; mechanical properties; X-ray optics; thin-film interfaces.