Arguing that the failure of instructional materials is frequently due to misconceptions held by their developers concerning the nature of comprehension, this chapter examines the factors involved in comprehension and relates them to the design of instructional materials. Three types of errors in comprehension are discussed, and ways to avoid them are presented: (1) instructional materials fail because of a lack of background, either already possessed by the student or to be provided by the materials; (2) instructional materials fail to provide a useful context for the instruction presented; and (3) instructional materials fail because of interference from various aspects of the instructional materials themselves. Some conclusions about comprehension are provided to aid in the designing of materials which avoid these problems. The text is supplemented with two figures, and an eight-item bibliography is provided. (Author/EW)