This thesis comprises three papers: a systematic literature review with thematic synthesis, a research study, and a critical appraisal of the research. In section one, the literature review, 18 research papers are analysed through thematic synthesis to examine the organisational factors within the NHS which impact psychological safety. NHS policies recommend having psychologically safe workplaces as they improve patient safety. The effects of organisational factors on psychological safety are unclear and understanding their impact can influence the effectiveness of future policies and interventions aiming to improve psychological safety. Four key themes were identified 1) organisational environment; 2) organisational structure; 3) organisational resource; and 4) organisational attitude which impact psychological safety. The clear identification of organisational factors in staffs’ experience of psychological safety must be considered in future NHS policy. In section two, the empirical paper, 11 semi-structured interviews with NHS operating theatre staff were conducted in line with grounded theory methodology and a model of understanding how psychological safety within NHS operating theatres was formed. The findings outline interacting factors at the individual, team, and organisational level which consider the impact of hierarchy, learning and relationships on the team being perceived as good. In addition, it offers an understanding of how patient safety and governance impact psychological safety within the operating theatre. The study suggests a need for NHS policy to consider the processes involved in improving psychological safety of staff. In section three, the critical appraisal, a summary of the research findings is presented along with personal reflections on the research process. This section includes consideration of the research findings within the wider context and offers recommendations for future research.