An attempt is made to elaborate a theoretical base about the functions and effects of embedded support devices (ESDs), considering the extent to which students actually use ESDs. ESDs are a set of activating, structuring, and motivating extras in study materials that are designed to support the individual study process. The report describes the set of ESDs that helps define the didactical elaboration of distance education courses at the Open University of the Netherlands (OU). Earlier research related to ESDs is reviewed, and a theoretical base is proposed. This base, which draws on a cognitive psychological framework, is then used to define the functions and the effects of ESDs, with a further description of methods used to research effects of ESDs. The framework takes into account the role of the reading process, motivation, individual differences, and the task environment. Seven figures and four tables illustrate the discussion. Two appendixes present information about OU publications and key concepts in the research. (Contains 108 references.) (SLD)