A half marathon is a road running event of 13.1 miles (21.1 km), typically run as a single loop course. The half marathon is the fourth most popular long-distance running event after the marathon, 10K run, and 5K run.
The half marathon distance has been run competitively since the early 20th century, with the first official world championship race being held in 1992. The half marathon is now an Olympic event, and is also included in the World Athletics Championships and other major international athletics competitions.