Under usual environmental conditions, exposure to the light-dark cycle and other zeitgebers entrains the circadian system to the earth’s 24-hr rotation to promote a species-specific environmental niche. However, circadian malsynchronization is a common condition which can have disastrous consequences. For example, chronic exposure to time zone transitions has been associated with cognitive deficits and menstrual cycle irregularities in airline personnel, and with reduced longevity in animal models. Approximately 20% of the world’s work-force are shift-workers, who have a higher prevalence of affective disorders, cancer, sleep disturbance, cardiovascular disease, and accidents compared with individuals on stable day-work schedules. Other circadian rhythm sleep disorders are also often associated with insufficient sleep and relatively high rates of mental illness. One of the most fundamental chronobiological tools for re-entraining the circadian system, and thereby alleviating related morbidity, is the phase-response curve (PRC) describing the magnitude and direction of circadian rhythm phase-shift, depending on the time of exposure to a zeitgeber. For example, the PRC for bright light is characterized by phase delaying effects of light administered before the nadir of the circadian body temperature rhythm, phase advancing effects after the temperature nadir, and smaller, often negligible, responses to light exposure in the afternoon. Although bright light is regarded as the most potent zeitgeber in humans, field studies have found less phase-shifting efficacy of bright light than might be predicted by laboratory experiments. Moreover, some individuals are relatively resistant to circadian synchronization to bright light, and bright light can have adverse side effects, including mania in individuals with a history of mania. Thus, there is a need to explore alternative or adjuvant zeitgebers. An extensive rodent literature has established that exercise also has a profound influence on circadian timing. There is also compelling, though not entirely consistent, evidence that exercise can elicit significant phase-shifting effects in humans. However, interpretation of the extant literature on the influence of exercise on the human circadian system has had many limitations, including poor control or measurement of other zeitgebers and masking stimuli; poor quantification or standardization of the exercise stimuli; and testing of insufficient numbers of subjects. Nonetheless, recent research has indicated a PRC for exercise in humans, which is of similar shape but lower amplitude than the bright light PRC. Moreover, consistent with hamster studies, there is evidence suggesting that bright light and exercise can have additive circadian phase-shifting effects, which could result in rapid correction of circadian rhythm disturbances.