Duathlon is an athletic event that consists of a running leg, followed by a cycling leg and then another running leg in a format bearing some resemblance to triathlons. The International Triathlon Union governs the sport internationally.

Duathlons are most similar to triathlons, with the key difference being the lack of a swimming leg. Another sport derived from triathlon is aquathlon, which combines swimming and running but has omitted the cycling part.

In this variation, the cycling and running segments need to be undertaken simultaneously by a team consisting of a predetermined number of individuals. Only one of the team members is running while all others are cycling. All the members of a team must be together at any given point of time but exchanging the tasks of running and cycling amongst the team members themselves is permitted.

The challenge is to rotate the task of running at an optimum rate such that the time from start to destination is minimized. This demands a smooth coordination amongst all team members which makes the sport more exciting. An example is the 100km-Duathlon around Dresden which is the oldest of its kind in Germany.