In the last decade there have been rapid developments in thefield of computer-based learning environments. A whole newgeneration of computer-based learning environments hasappeared, requiring new approaches to design anddevelopment. One main feature of current systems is thatthey distinguish different knowledge bases that are assumedto be necessary to support learning processes. Currentcomputer-based learning environments often require explicitrepresentations of large bodies of knowledge, includingknowledge of instruction.This book focuses on instructional models as explicit,potentially implementable representations of knowledgeconcerning one or more aspects of instruction. The book hasthree parts, relating to different aspects of the knowledgethat should be made explicit in instructional models:knowledge of instructional planning, knowledge ofinstructional strategies, and knowledge of instructionalcontrol. The book is based on a NATO Advanced ResearchWorkshop held at the University of Twente, The Netherlandsin July 1991.