Zeitgebers are external cues that the circadian rhythm uses to maintain a 24-hour cycle. Zeitgebers provide information about the external clock. The body uses this information to synchronize the circadian rhythm with external time. The most significant zeitgeber is light. Food, exercise, social interactions, temperature, atmospheric conditions are other zeitgebers.

Zeitgeber, which means "time giver," is one of the essential terms of chronobiology. Zeitgebers are environmental stimuli that give the body a hint on the day/night cycle. Light is the most significant zeitgeber of all; however, other zeitgebers are temperature, exercise, meal timing. Zeitgebers are crucial for synchronizing the internal clock with the external clock.