This chapter introduces basic concepts related to the structure of crystalline solids. This includes the difference between single-crystalline, polycrystalline, and amorphous materials; the description of periodic crystals in terms of a Bravais lattice and an atomic basis; and surveys of the 14 Bravais lattices in three dimensions as well as the 5 Bravais lattices characterizing two-dimensional crystals. The chapter concludes with an introduction to the terminology of Miller indices for describing lattice planes and directions. This chapter—and indeed all chapters of the book—also provides sets of key references, end-of-chapter problems, and a detailed glossary of technical terms, aimed at facilitating the learning of new concepts and practicing problem-solving.