In car design, ground effect is a series of effects which have been exploited in automotive aerodynamics to create downforce, particularly in racing cars. This has been the successor to the earlier dominant aerodynamic focus on streamlining. The international Formula One series and American racing IndyCars employ ground effects in their engineering and designs. Similarly, they are also employed in other racing series to some extent; however, across Europe, many series employ regulations to limit its effectiveness on safety grounds.

Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case. For some classes of racing vehicles, it may also be important to produce downforce to improve traction and thus cornering abilities.