This chapter describes the operation of various forms of phase-change memristive devices and systems, evaluating their fundamental behaviour and outlines their possible advantages and disadvantages compared to more usual implementations. It introduces and demonstrates experimentally a new and simple approach to providing non-volatile logic operations, specifically AND and OR Boolean logic, using phase-change devices. Chalcogenide materials enables several novel device concepts, such as phase change memories (PCMs), optical disks and electronic threshold switches for high-current select devices in crossbar arrays. The chapter proposes an integrated, all-photonic memory employing phase-change materials in combination with silicon nitride waveguides. It shows that it is possible to have sub-nanosecond, high speed, multi-level memories in …