A running board is an accessory car part that is located beneath the doors on the side of a vehicle. A running board is both fashionable and practical and looks like a narrow step. Running boards are typically made of chrome or fiberglass. Many vintage cars feature running boards and many custom trucks and SUVs feature running boards that are not only installed as part of a custom look, but also as a step for easier entrance and exit.

A running board, also sometimes called a nerf bar, footboard, or simply truck steps, is typically not a factory feature but rather a custom feature added after the fact. Running boards are most frequently seen on full-size pickup trucks and sport utility vehicles and sometimes on full-size conversion vans. Though a running board serves no practical purpose on a car, it is not uncommon for a customized car to have running boards.

Originally, early model cars featured a running board on both sides of the vehicle. Vintage cars sat higher off the ground than modern cars and so the running board served as a step to provide sure footing for entrance. When the earliest hotrods began to hit the street, they were often cars with the fenders and running boards removed.

Though custom cars became popular in the 1950s, it is a practice that has only increased in popularity. A modern customization of any vehicle may include the addition of running boards. Full-size trucks are often seen with chrome running boards, but on a car with a custom paint job, the running boards are usually fiberglass and painted to match. On cars, especially low riders, a running board is merely a fashionable customization. In addition to the various designs and finishes, a running board may even be lighted.

The addition of a running board can be accomplished by either the vehicle owner or at a body shop that customizes cars. A running board may be classified as a truck or vehicle accessory or body part. They can be purchased either through a body shop or through any number of catalogue and online retailers.