AbstractPhase Change Materials are adopted in optical data storage and are currently evolving to become the active material of a new viable non‐volatile memory technology which is expected to eventually replace no‐longer‐scaling Flash memory technologies. Phase‐Change Memories store their information as the material phase of a chalcogenide metal alloy (high‐resistive amorphous, respectively low‐resistive crystalline phase), the most important compound being Ge2Sb2Te5(GST). To give insight in this important evolution, the paper describes the different aspects of Phase‐Change Memories. It starts from basic operation principle and fundamental material properties (Sections 2 and 3). Vital to their operation are not only the vitrification and crystallization properties of the chalcogenide material, but also the phenomenon of electronic threshold switching enabling low‐voltage Joule heating in the amorphous phase. Understanding and modeling of these effects are described in Section 4. Cell concepts and integration technology aspects, including optimization schemes aimed at reducing the program current are covered in Section 5. Finally, the excellent reliability and scaling properties of Phase‐Change Memories are discussed in Sections 6 and 7. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)