Caring for a new child is a significant, demanding, and time consuming role, often associated with increased stress. Postnatal depression is one possible outcome of increased stress and research has highlighted the importance of detecting depression in new mothers. However fatigue a correlate of depression, has only recently become a focus of research among health professionals. Understanding the nature of fatigue and its management within the postnatal period, the focus of this study, may reduce its impact on women’s lives. This longitudinal study explores changes in intensity, physical, mental and emotional dimensions of fatigue, factors associated with higher levels of fatigue, the impact of fatigue on women’s usual activities, and strategies for managing fatigue. Self-administered structured questionnaires gathered data form 504 women at 1, 6, 12 and 24 weeks after birth. Reliable and valid instruments were used to measure the relationship between the defined factors and the outcome of fatigue at the various time points. State anxiety was a consistently strong predictor of fatigue intensity across time and group. Women sought to manage their fatigue by using self-care practices and asking for help from family and friends. This research highlights two issues for health professionals – care of new mothers must include recognition that higher levels of state anxiety are associated with higher levels of postnatal fatigue: ongoing assessment of fatigue and the strategies used to manage it is essential beyond the early postnatal period / Doctor of Philosophy (PhD)