Data is the raw material of Visualization in Scientific Computing (ViSC). ViSC seeks to transform calculated or measured data into graphical forms better suited for interpretation. Data is the lifeblood of any visualization system, and its representation must support structures appropriate to scientific computing as well as graphical forms. This representation must also permit efficient transport and storage. We discuss Flux, a general data format supported by the apE, a flexible visualization environment developed at the Ohio Supercomputer Center. Flux effectively represents grids, volumes, polygonal objects, images, motion paths, particles, and other structures, in a format which is both portable and compact. The format is also suitable for dynamic transport in a data flow system. The Flux format has been designed with significant participation from the scientific community, and will be compared with other data representations currently in use. The implementation of the format on a wide variety of mainframes and workstations will also be presented,as well as a series of examples from a variety of scientific applications. The Flux format will be shown to be a flexible solution to the problems of data representation for scientific visualization.