Mud flaps are rubber mats attached directly behind the wheels of cars and trucks. The main function of mud flaps is to shield other cars from mud and other debris flung out by tires. Quite often in off-road or rainy conditions, car and truck tires are partially submerged and centrifugal force will send mud and debris towards the back of the vehicle. Although they are officially called mud flaps, these rubber mats also deflect loose gravel and excessive rainwater.

Mud flaps are not always standard accessories for passenger vehicles, but almost all commercial trucks use them as safety features on the road. Trucks hauling loose materials such as gravel must take precautions against accidents caused by flying debris. The use of mud flaps on commercial vehicles may even be mandated in some areas.

As with many other after-market vehicle accessories, mud flaps have become popular means of self-expression. Automotive supply stores carry a wide variety of mud flaps which feature cartoon characters, familiar logos and short sentiments similar to bumper stickers. Some companies actually commission custom mud flaps which feature their name and contact information. Installation of mud flaps is usually not difficult, but it can be very messy and awkward. A few bolts or screws hold the top of the mud flap to the frame and the bottom edge remains unattached.

Mud flaps perform a useful service, but they are by no means a requirement for safe driving. Car owners may discover that these flaps help to keep the undercarriage of the vehicle cleaner by rerouting sprays of muddy water. Small objects on the highway may be kicked up by the tires, but mud flaps prevent further damage. Many drivers who do not use mud flaps may discover a distinctive pattern of splattered mud behind each wheel well. Small nicks and scratches caused by flying debris may also be prevented with the addition of quality mud flaps.