A car platform is a shared set of common design, engineering, and production efforts, as well as major components, over a number of outwardly distinct models and even types of cars, often from different, but somewhat related, marques. It is practiced in the automotive industry to reduce the costs associated with the development of products by basing those products on a smaller number of platforms. This further allows companies to create distinct models from a design perspective on similar underpinnings. A car platform is not to be confused with a platform chassis, although such a chassis can be part of an automobile's design platform, as noted below.

A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, seat one to eight people, have four wheels, and mainly transport people, not cargo.