Long-haul crew experience regular misalignment of the circadian rhythm causing several jet lag symptoms. However, it is unclear whether melatonin acrophase shifts post-trip relate to perceived jet lag. In addition, the role of psycho-behavioural variables on the relationship between subjective and objectively measured jet lag and fatigue are largely ignored. Further, recent research indicates that the timing of meals may help reduce jet lag symptoms on days off. The overall aim of the thesis was to give a comprehensive account of jet lag in long-haul cabin crew in terms of the relationship between bio measures and symptom perception. Four studies were undertaken. In Study 1 (longitudinal), 35 long-haul crew completed measures of circadian preference, coping, stress arousal, objective sleep parameters and subjective jet lag. The results found that i) symptoms of jet lag were worse on the day crew returned home and ii) perceived lower appetite than normal and restless sleep (objective) predicted subjective jet lag. In Study 2 (longitudinal, N = 28), circadian phase [melatonin acrophase (peak time)] was also measured. The results found a discrepancy between subjective jet lag change scores and circadian phase change post-flight predicted by perceived lower appetite than normal. In Study 3 (cross-sectional), 95 crew completed measures of illness cognitions, coping, social support, pre-work strategies, subjective jet lag and fatigue. Timeline predicted subjective jet lag, consequences predicted subjective fatigue whereas a reduction in multidimensional jet lag was predicted by increased social support. In Study 4 (randomized controlled trial, N = 60), half the participants formed an implementation intention to eat regular meals on days off (intervention) and half did not (control). Pre-intervention measurements were taken at baseline and post-intervention measures on the second recovery day. Formation of an implementation intention to eat regularly resulted in a reduction of jet lag (unidimensional) but not multidimensional jet lag and objective alertness (PVT). These findings demonstrate that jet lag is in part a psycho-social construct, not just a biological one, which is influenced by sense making and can be moderated through diet. The results have important practical and theoretical implications.