Exactly what is it that illustrations do? Instructional graphics have an impressively large amount of research behind them, which we can summarize only briefly here. The overwhelming majority of that research was conducted with print materials, and we realize that not all findings will generalize to screen display perfectly. Nevertheless, we believe it instructive to examine some of the generalizations coming from that research. Several authors have speculated on the functions of pictures. While their conclusions are not in complete agreement, neither are they contradictory. Rather, they usually emphasize slightly different things. p. 1 of 4