Creating high-quality multimediapresentationsrequiresmuch skill, time, and effort. This is particularly true when temporal media, such as speech and animation, are involved. We describe the design and implementation of a knowledge-based system that generates customized temporal multimedia presentations. We provide an overview of the system's architecture, and explain how speech, written text, and graphics are generated and coordinated. Our emphasis is on how temporal media are coordinated by the system through a multi-stage negotiation process. In negotiation, media-specific generation components interact with a novel coordination component that solves temporal constraints provided by the generators. We illustrate our work with a set of examples generated by the system in a testbed application intended to update hospital caregivers on the status of patients who have undergone a cardiac bypass operation.