AbstractDue to their unique ability to provide a variety of gear ratios in a very compact space, planetary gear systems are seen in many applications from small powered screw drivers to automobile automatic transmissions. The versatile planetary gear device is often studied as part of an undergraduate mechanical engineering program. Textbook presentations typically illustrate how the different planetary gear components are connected. Understanding of the operation of the planetary gear set can be enhanced using actual hardware or simulations that show how the components move relative to each other. The Department of Engineering Mechanics at the United States Air Force Academy has developed a computer simulation of the planetary gear set and the Chrysler 42LE automatic transmission. Called “PG‐Sim,” the dynamic simulations complement a static textbook presentation. PG‐Sim is used in several of our courses and assessment data clearly indicates students' appreciation of its visual and interactive features. In this paper, we present an overview of PG‐Sim and then describe how the simulation courseware facilitates understanding of the planetary gear system. © 2003 Wiley Periodicals, Inc. Comput Appl Eng Educ 11: 144–155, 2003; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.10045