Autocross is a form of motorsport in which competitors are timed to complete a short course using automobiles on a dirt or grass surface, excepting where sealed surfaces are used in United States. Rules vary according to the governing or sanctioning body, such as the length of the course, the number of permitted attempts, or whether competitors start the course individually at intervals or at the same time as others. In this latter form, Autocross differs from other forms of motor racing by using a system of heats or alternative timing methods for the classification rather than racing for position and declaring the first across the finish line as the winner.

Autocross began in the United Kingdom in the early 1950s at an amateur level within local motor clubs using temporary courses marked on grassy fields to not cause damage to any cars. The creator of rallycross, Robert Reed, wanted a version of autocross with more spectator-appeal to be made for television, using professional racing and rally drivers and teams; and courses featuring jumps, sharper corners and a mixture of sealed and unsealed surfaces.

In the United States, the motorsport called autocross is more like the UK and European sport of autotesting or autoslalom, and what is called rallycross in the US is more like what the UK and Europe call autocross. The Sports Car Club of America (SCCA) publishes rules for autocross, which are also used by many independent clubs, as well as hosting national events and championships within its Solo branded series. The National Auto Sport Association brands its version of US-style autocross as NASA-X, Both take place on sealed asphalt or concrete surfaces, one car at a time running against the clock, with traffic cones defining the path to be driven, and an emphasis on car handling and precision manoeuvring.

Autocross courses can be as short as 800 metres or several kilometres long. Courses may be temporary and marked by traffic cones which can be reconfigured during events, or be permanent tracks with approval by a motorsport body.

Events typically have many classes that allow almost any vehicle, from production touring cars to purpose-built racing cars. The international body for autocross, the FIA, and the French body, FFSA, both provide technical specifications for cross cars, lightweight buggy cars.

Autocross is sanctioned in Australia by MotorSport Australia, where it is defined as an event held on a course less than four kilometers long. Vehicles are timed during each pass of the course and results are typically tallied over a number passes. Eligible vehicles include regular road-going cars, purpose-built buggies and full racing or rallying-prepared machines. Many events allow junior participants as low as 14 years old.

American autocross events (also called "Solo", Auto-x" or "Autoslalom") are typically held on flat, paved surfaces such as parking lots or airport tarmacs, and usually have a new course for each event, marked by traffic cones.

Autocross is one of the most accessible and affordable forms of motorsport, and autocross events are open to novices. Because autocross events use rubber traffic cones to define the course, and are typically run on paved surfaces with few obstructions, the hazards and barriers to entry are low. While speeds are generally no greater than those encountered in legal highway driving, the combination of concentration and precision manoeuvring gives drivers an experience similar to that of a full road course race.