Oxide materials are good candidates to replace Si devices which are facing performance limits since these materials display unique properties, either due to their composition design and/or doping technique.  The author introduces a means of selecting oxide materials according to their functions and explains metal/oxide interface physics. Material development is the key to matching oxide materials to specific practical applications.In this book, the investigation and intentional control of metal/oxide interface structure and electrical properties with the data obtained using non-destructive methods such as x-ray photoelectron spectroscopy (XPS) and x-ray reflectometry (XRR) are discussed. Oxide materials should support the development of future functional devices with High-k, ferroelectric, magnetic and optical properties. Optical sensors as an application of metal Schottky contact and metal/oxide resistive random access memory structure are also explained.