Introduction.

When a coherent superposition of Rydberg states is excited by a laser pulse, a Rydberg wave packet is created. These wave packets are supremely quantum mechanical objects. However, they can be constructed to display classical, nearly classical, or semiclassical behavior, and thus serve as a natural bridge between the microscopic and mesoscopic worlds. In addition, their comparative simplicity allows detailed studies of the fundamental interactions of light with matter. The authors of this focus issue were invited to submit papers that reflect both the range of dynamical behavior exhibited by Rydberg wave packets, and the depth of understanding of them that is possible with current experiments and theory. In particular, the papers in this issue illustrate the possibility that emerging laser technology can be used not only to observe quantum behavior, but also to control it.