Modified stock car racing, also known as modified racing and modified, is a type of auto racing that involves purpose-built cars simultaneously racing against each other on oval tracks. First established in the United States after World War II, this type of racing was early-on characterized by its participants' modification of passenger cars in pursuit of higher speeds, hence the name.
There are many sanctioning bodies for modifieds, each specifying different body styles and engine sizes.
Modified racing began as race drivers modified their cars to gain a competitive advantage over their fellow competitors. What started out as minor modifications to the cars has now grown to the point that some modified classes are no longer based on any current production vehicles. NASCAR was instrumental in modified racing's beginnings. Some of NASCAR's pioneers were veteran modified racers long before NASCAR's inception in 1949. As time progressed, modifieds grew away from "strictly stock" or "stock cars", and became akin to both stock cars, and open-wheel cars. Today's supermodifieds have more in common with Indy cars than they do stock cars.