Phase change materials are characterized by the existence of at least two different phases, between which it is possible to reversibly and repeatedly switch in a very short timescale. Large variation of the electrical and optical properties occurs upon phase change. These unique properties have made phase change materials very attractive for the realization of nonvolatile electronic memories based on the concept of using the reversible amorphous-to-crystalline phase transition as writing and erasing mechanism. The two logic states are the high resistance, low reflectivity amorphous phase and the crystalline, high reflectivity, low resistance phase. The switching can be obtained either by using a laser pulse or an electric pulse.The technological success of phase change materials was firstly linked to the realization of optical memories, and it was enabled by the discovery of a class of materials, belonging to the pseudobinary line GeTe-Sb2Te3, characterized by large variation of optical contrast by laser pulses. Thanks to the use of such materials, the rewritable optical storage technology has been developed, reaching its third generation of blu-ray disks with 100 Gb capacity. The most common used material for optical disks has composition Ge2Sb2Te5 and it is also characterized by order of magnitude of resistance variation when changing from amorphous to polycrystal, with face centered cubic structure (fcc). Following the optical memory concept, the phase change materials have been proposed for the realization of nonvolatile memories based on the phase transitions driven by electric pulses. Phase change memories (PCM) employing …