This paper presents the updated (fourth generation) version of the instructional design (ID) model, noting its emphasis on a scientific, iterative approach based upon research and theory in learning and instruction and upon applied development experience. Another important trend toward a scientific approach to instructional design is the increased emphasis placed on the use of evaluation not as a last step but as an integral part of the design system. The various facets and combinations of the updated ID process (Analysis, Analysis-Design, Analysis-Maintenance, Design, Design-Development, Design-Development-Implementation, Development-Implementation, Development-Implementation-Maintenance, Implementation, Implementation-Maintenance, and Maintenance) are presented in terms of the authoring activities associated with each facet. A diagram of the model is included. (6 references) (GL)