The silicon at the heart of highperformance integrated circuits (ICs) is the most precisely engineered material in mass production today. Crystalline silicon, purified to the level required for manufacturing modern, high-performance microelectronics (better than parts-per-billion purity), is arguably the most perfect material known. It is produced in large quantities and very economically. Continuing progress in basic silicon materials science has been central to this achievement. At the same time, access to such a perfect material and detailed knowledge of silicon's properties have provided the experimentalist with excellent opportunities to devise rather elegant experiments in whichthe parameters can be controlled very precisely. Silicon has similarly provided condensed-matter theorists with a nearly ideal test bed for new theoretical approaches. This issue of MRS Bulletin is dedicated to the materials physics that has both enabled the development of such a highly perfect material and benefited from its availability.