Law enforcement has been classified as one of the most stressful professions in the world. It has been demonstrated that if not managed effectively, stress has a significant negative impact on the physical health and psychological well-being of police officers. The aim of this thesis is to increase understanding of protective and enabling factors that facilitate police work, particularly in the speciality assignment of undercover work. Chapter 1 introduces literature on common stressors in police forces and specific stressors which can affect undercover agents, outlines the negative impacts these can have on individuals, and concludes with a discussion about the importance of coping and resilience within police forces. Chapter 2, a systematic literature review, examines and synthesises the literature on resilience and coping in police officers, when dealing with stress. Eighteen studies were included in the final review, from different countries and with large/diversified samples. Chapter 3 presents a critique of the Resilience Scale (RS; Wagnild & Young, 1993); a 25-item self-report assessment tool that measures the degree of individual resilience. The psychometric properties of the RS are discussed, and recommendations are made as to how the measure could be improved. Chapter 4 consists of an empirical study using a convergent mixed methods approach to examine resilience, coping, and detection avoidance strategies used by police officers with and without undercover/plainclothes experience. A total of 139 Portuguese police officers, working in criminal investigation, provided some form of data towards this study. Finally, Chapter 5 discusses the work presented, drawing together the main findings and limitations from each chapter. Implications for practice within police forces, ways in which psychologists can support and increase well-being in police officers (particularly undercover agents), and recommendations for future research are also presented