The clinical information environment is of a heterogeneous nature. A hypermedia information system is a means for integrating different types of data and knowledge a clinician needs for making his clinical decisions. An integrated multimedia system with various kinds of knowledge processing and decision support components as well as clinical registries is supposed to be the “intelligent” clinical assistant system of the future. Various knowledge based systems have to communicate with other (not necessarily knowledge based) components of a clinical information and communication system in a hypermedia network. A decisive step towards a realization of this vision is the progress in structuring and modelling medical knowledge. The success of introducing knowledge based products in everyday clinical practice depends on their degree of flexibility in use and integration in a clinicians work.