Multimedia presentation technology has enormous potential for a myriad of applications including academic classrooms, industrial training, and business presentations. As presentation technology advances, it is possible to incorporate a wider range of media including variable duration media such as simulations and animations. At the same time, users are able to take more control over presentations by controlling the rate and selection of media being played. To make full use of these advances, multimedia systems must support flexible presentations that incorporate many variations in the way they are played. This paper identifies three requirements for flexible presentations and derives four requirements for synchronization of flexible presentations. The paper presents FLexible Interactive Presentation Synchronization (FLIPS), a model for specifying coarse synchronization for flexible presentations. FLIPS supports a wide range of temporal synchronization specifications. It also provides algorithms for attaining a consistent and coherent presentation state in response to user interaction (e.g., skipping to a different slide or selection) and other state-changing events. Applications of the FLIPS model are discussed.