Simple Shear 98 is a computer program with graphical user interface that was developed to aid beginning geologists in understanding the mechanics of simple shear. It was created using Visual Basic 5, an object oriented intermediate-level programming language, and will run on any PC using Windows 95 or NT 4. The program displays data to the user through two windows, one a strain grid and the other a table of coordinates. The user picks one of several objects to strain from a drop down menu, and is allowed to input shear strain values. Following each increment of strain instigated by the user the program calculates and displays elongation, stretch, quadratic elongation, and angular shear strain values. Finally, progressive simple shear can be visualized through a movie function. The following six key concepts can be illustrated through the use of Simple Shear 98: (1) Individual material particles are translated linearly in planes parallel to the direction of shear. (2) Line segments rotate about the intermediate principal strain direction in a clockwise sense for dextral shear and in a counterclockwise sense for sinistral shear. (3) Lines that lie in the NE and SW quadrants undergo elongation, whereas lines that lie in the NW and SE quadrants undergo shortening during dextral sense progressive simple shear. During sinistral simple shear these conditions are reversed. ( 4) Angles between adjacent line segments undergoing shortening become larger while angles between adjacent line segments undergoing extension become smaller. (5) Lines rotate toward the direction of shear but never reach it. (6) Under the right geometrical conditions, simple shear can produce very unusual results such as the nearly complete unfolding of a fold.