From the earliest stages of elementary school to the advanced college level, vari­ ous types of illustrations are included in educational materials in order to pro­ mote learning. These illustrative adjuncts are often profuse and, in many cases, they may be the most striking feature that distinguishes one set of learning materials from another. In addition, the perceived effectiveness of the illustra­ tions clearly plays an important role in the marketing of many educational materials. Despite this pervasiveness and salience in education, there has never been a systematic effort to bring together the results of research on illustrations in order to provide some level of guidance to the developers of commercial learning materials. There is, however, a considerable research literature that is directly relevant to this aspect of education. The purpose of the present two­ volume set is to summarize and interpret the existing research literature that deals with the various educational functions of illustrations. In undertaking to produce an omnibus reference work on psychological and instructional issues surrounding illustrated learning material, our paramount aim has been to stimulate closer collaboration between researchers, producers, and users of educational text. The problems associated with moving the findings of educational research into the realm of everyday practice have been perennial ones. While many researchers and practitioners are interested in fundamentally similar questions, they typically speak dissimilar languages, read different jour­ nals, and carry out their work under disparate ideologies.