  Localized quantum wave packets can be produced in a variety of physical
systems and are the subject of much current research in atomic, molecular,
chemical, and condensed-matter physics. They are particularly well suited for
studying the classical limit of a quantum-mechanical system. The motion of a
localized quantum wave packet initially follows the corresponding classical
motion. However, in most cases the quantum wave packet spreads and undergoes a
series of collapses and revivals. We present a generic treatment of wave-packet
evolution, and we provide conditions under which various types of revivals
occur in ideal form. The discussion is at a level appropriate for an advanced
undergraduate or first-year graduate course in quantum mechanics. Explicit
examples of different types of revival structure are provided, and physical
applications are discussed.
