The first section of this pamphlet illustrates and describes the overhead projector, and discusses several of its advantages over other projection devises, including its simplicity of operation, conservation of class time, dynamic effects, image size, etc. The second section describes in some detail materials and methods used to make visuals, then discusses ways to employ visuals more effectively, with suggestions on the use of color, printing and lettering, and overlays. Loose, hinged, rotating, sliding, and masked overlays are described, and an example is shown of how to use a series of overlays to illustrate a mathematical identity. Finally, there is a summary of indirect processes for making overlays from textbooks, magazines, and other printed material, when heat, diazo, photocopy, electrostatic, or lift processes may be used. Section 3 discusses how to design an effective visual once the purpose is determined, then describes and illustrates the development of six different sample visuals. Section 4 suggests additional uses for overlays--explaining mathematical tables, discussing homework problems, writing test questions, illustrating locus problems, showing transparent models, silhouettes, moving elements, ripple tanks, etc. Section 5 lists references, research publications, and sources of equipment and materials. (CR)