Race courses are usually held through the streets of major cities and towns but could be on any sealed road.
Distances can be any distance, usually at least 1500m or a mile, some courses are standard distances (e.g. 5km or 10km) however many courses are odd distances as they start and or finish at local geographic features, for example "Bay to Breakers" or "City to Surf" and are named accordingly.
The Marathon and half marathon is a common distance for road races (e.g. London Marathon or Boston Marathon. Ultramarathons cover distances of more than 50km and can be hundreds of kilometers and take many days to complete.
Courses may take any route conceivable such as out and back, point to point, a loop, multiple loops, figure eight or combinations of these.
The Olympic Marathon and World Marathon Championships and Half Marathon Championships held by the IAAF are the major "official" road running competitions.
To the competitive runner road running offers many challenges, hills, sharp bends, various pavement, large crowds, the weather and other competitors tactics. As most courses are middle distance or long distance Aerobic fitness is most important, Anaerobic abilities are also used on hills, mid race surges and over the final stages of the race. Mental tenacity is also very important to be successful.
To the recreational or "fun runner" fitness is quickly improved and can be a very social sport with large training groups common.
Large road races are often wider community events and they often highlight or raise money for an issue or project.