Materials under pressure. This issue of MRS Bulletin focuses on several of the many and diverse domains of advanced materials research where applied pressure or stress is used to alter or garner information on material properties. The application of high pressure—often combined with high temperatures and advanced analysis—has led to important technological progress. The cover shows a diamond anvil cell used to apply high pressures to materials. The diamond is 2.5 mm in height. A sample chamber is formed between the anvils inside a gasket made of rhenium metal. The diamond windows are transparent to a wide region of the electromagnetic spectrum for probing chemical reactions at high pressures and temperatures with UV–VIS–IR, lasers, neutrons, ultrasound, and x-rays or other forms of radiation. Image courtesy of Steven D. Jacobsen, Northwestern University. See the technical theme that appears on page 710.