The Houston Marathon is an annual marathon usually held every January in Houston, Texas, United States, since 1972. With thousands of runners and spectators, it is the largest single day sporting event in the city. It is run concurrently with a half marathon and a 5 km race. The 2007 race included the first-ever satellite running of the event, run simultaneously in Fallujah, Iraq.

A half marathon is a road running event of 21.0975 kilometres —half the distance of a marathon. It is common for a half marathon event to be held concurrently with a marathon or a 5K race, using almost the same course with a late start, an early finish or shortcuts. If finisher medals are awarded, the medal or ribbon may differ from those for the full marathon. The half marathon is also known as a 21K, 21.1K, or 13.1 miles, although these values are rounded and not formally correct.