The articles in this Special Issue of physica status solidi (b) represent the latest progress in the field of science of phase-change materials, in particular amorphous chalcogenides. The status of their current commercial as well as forthcoming applications in digital memory, including re-writable optical discs, such as digital versatile discs, and flash memory is described. The contributions are dedicated to Stanford R. Ovshinsky, a pioneer of science and applications of disordered materials and the inventor of phase-change memory. They have been written by many of his admirers and followers (see the Preface by A. V. Kolobov and M. Popescu on pp. 1824–1826).