This paper presents an approach for developing flexible Hypermedia Learning Environments (HMLE) and applies this theoretical framework to the creation of a layered model of a hypermedia system, called HyperDisc, developed at the German Institute for Research on Distance Education. The first section introduces HMLE and suggests that existing hypermedia systems often suffer from theoretical, conceptual, and methodological shortcomings. The empirical background of hypermedia use and hypertext-based technologies are discussed in the second section. The next section deals with design features crucial for flexible HMLE, following a model for describing computer-based systems that comprises learner, subject matter, pedagogic-didactic, and information technology components. The fourth section presents the HyperDisc program as a prototype of HMLE intended to cope with design requirements outlined for fostering open and flexible learning; features discussed include expository learning activities, exploratory learning activities, expressive learning activities, and openness (i.e., the potential to integrate and create new contents). A figure illustrates the main screen of HyperDisc. Contains 14 references. (DLS)