Instructional pictures may be classified on the basis of how they convey meaning including classification as representational, analogical, or arbitrary (Gropper, 1963; Know!ton, 1966). Some previous reviews of picture effects have dealt with only the first category of pictures -that is, pictures that are isomorphic with the objects or concepts that they represent (Alesandrini, 1982;Levin and Lesgold, 1978). Other reviews have also considered arbitrary or non-representational pictures such as flowcharts and graphs (Levie and Lentz, 1982;Macdonald-Ross, 1977a). This article discusses research on all three types of pictures and considers how each type may play a crucial, yet different, role in the learning process. The focus is on picture effects in adult meaningful learning such as concept learning, learning from prose materials, and learning from expository text.