A review of research on factors involved in general reading ability and reading in the content areas is presented. In the primary grades, reading comprehension appears to be a specific factor dependent on instructional conditions. During the intermediate grades, common factors emerge and tend to integrate at a more central response level and become common to a variety of reading situations. Factors identified as underlying general reading comprehension at grade 6 appear to be the same as those that emerge at the high school level. General reading ability draws upon factors in the cognitive, linguistic, perceptual, and affective domains. Reading in the content areas draws to some degree upon common factors and to some degree upon specific factors, particularly when comprehension tasks involve skills such as data interpretation. Studies have indicated that when specific vocabulary and purposes of content reading were stressed, gains in comprehension were noted. Self-selection of content area materials also enhanced comprehension. It was recommended that reading ability should be assessed separately in specific content areas. However, continued stressing of reading in the content areas as part of a developmental reading program may alter the present concept of general reading ability and its assessment. Bibliography is included. (WB)