The experimental CAI system which is being tested at Delft University of Technology is structured in a modular manner to account for high changeability. The concept formulated for this project was the outcome of research into technological, organizational, and educational developments in CAI, and the enumeration of the common aspects of the courseware, different author languages, systems, and methods in current use. This paper discusses this concept and the implementation of the system, including the presentation of lessons, recording activities, designing a lesson, evaluation, distribution of data, and management. While experience with large numbers of students and course authors is not yet available, the system is functioning technically in accordance with expectations at this time. It is expected that it will be used more extensively by lecturers and students at the university in the future, and that extensions in the form of a compiler for the TUTOR subset and the CAISCO interpreter for a microcomputer system will make it possible to test the changeability and flexibility of this modular system. (JEG)