Discusses the need for and use of models in the design and development of instructional materials, providing an overview of the main characteristics of a unit model and three course models: a simple linear model, a refined linear model, and a branched model. (RAO)

The second in a series of short descriptive papers concerning Britain's newly-established Open University. The author discusses the nature of the teaching materials being developed by the university and some of the difficulties involved in producing these materials. (AK)