Lines are elemental design devices that provide the primary structure for visual expressions in printed media. Gestalt principles of perception emphasize the role of the viewer, so the energy of the lines and the commercial viability of a particular design depend upon the designer's and photojournalist's understanding of both the viewer's programed response to lines and his or her mental set. Although the roles of intuition and "previsualization" are debated, the mechanical nature of mass media and the common link of realism probably make previsualization more important for the designer and photojournalist. The complex relationship between form and content that results when photographs are printed in the mass media depends upon cropping as well as upon lines and shapes. Framing is nothing more than the lines that mark the border between artifact and environmental space or image and border. Lines are also the primary tool of previsualization, and necessary in the creation of three dimensional effects. As physical events, lines represent a balancing of compositional forces, and they can also be perceived temporally. Although photojournalists discover lines while designers create them, students in both disciplines can benefit by instruction in their use. (A slide presentation outline is appended.) (JL)