A half marathon is a road running event of 21,097.5 meters, or 13+7⁄64 miles, about 13.1 miles. It is half the distance of a marathon and usually run on roads. It is a popular race for runners of all abilities, long enough to be a serious challenge for most people, but not requiring the level of training of a marathon.

In consequence, many towns and cities hold annual all-comers half marathon races through their streets. It is also common for a half marathon event to be held concurrently with a marathon, using almost the same course with an early finish.