A model for knowledge representation that incorporates structure and time is presented. The model is the domain of structured histories, which is based on the interleaving of these features in a nested, structured manner. A rich temporal representation language is provided. The interleaving structure and time is shown to be fundamental to the representation of a variety of temporal domains, including planning, knowledge bases, and design. Applications in the areas of databases and music processing that are based on the structured histories ontology are summarized. The novelty of the approach presented in this paper is in the design of a general, domain independent, representation scheme for capturing the aspects of structure and time. As a result, both aspects can be declaratively specified in a single logical design, thereby providing a basis for well founded processing of structured - temporal domains.