The appearance of heavy duty trucks has begun to change due to manufacturers' efforts to improve truck aerodynamics. The need to make trucks more aerodynamic has come from higher fuel costs and the owners' need to stay cost-competitive. Improving the aerodynamics of Class 8 trucks is not simple. It requires an understanding of the aerodynamics involved, the tests needed to evaluate the vehicle shape changes, and valid estimates of the vehicle operational cost savings. This paper supplies the reader with an introductory discussion in these areas, covers the basics of heavy duty truck aerodynamics, and explains some of the current data available for improving truck aerodynamics.