Background: Shared values, norms and beliefs of relevance for safety in health care can be described in terms of patient safety culture. This concept overlaps with patient safety climate, but culture represents the deeprooted values, norms and beliefs, whereas climate refers to attitudes and more superficial manifestations of culture. There may be numerous subcultures within an organization, including different professional cultures. In recent years, increased attention has been paid to patient safety culture in Sweden, and the patient safety culture/climate in health care is regularly measured based on the assumption that patient safety culture/climate can influence various patient safety outcomes. Aim: The overall aim of the thesis is to contribute to an improved understanding of patient safety culture and subcultures in Swedish health care. Design and methods: The thesis is based on four studies applying different methods. Study 1 was a survey that included 23,781 respondents. Data were analysed with quantitative methods, with primarily descriptive results. Studies 2 and 3 were qualitative studies, involving interviews with a total of 28 registered nurses, 24 nurse assistants and 28 physicians. Interview data were analysed using content analysis. Study 4 evaluated an intervention intended to influence patient safety culture and included data from a questionnaire with both fixed and open-ended questions, which was answered by 200 respondents. Results: A key result from Study 1 was that professional groups differed in terms of their views and statements about patient safety culture/ climate. Registered nurses and nurse assistants in Study 2 were found to have partially overlapping norms, values and beliefs concerning patient safety, which were identified at individual, interpersonal and organizational level. Study 3 found four categories of values and norms among physicians of potential relevance for patient safety. Predominantly positive perceptions were found in Study 4 concerning the Walk Rounds intervention among frontline staff members, local managers and top-level managers who participated in the intervention. However, there were also reflections on disadvantages and some suggestions for improvement. Conclusions: According to the results of the patient safety culture/ climate questionnaire, perceptions about safety culture/climate dimensions contribute more to the rating of overall patient safety than background characteristics (e.g. profession and years of experience). There are differences in the patient safety culture between registered nurses and nurse assistants, which imply that efforts for improved patient safety must be tailored to their respective values, norms and beliefs. Several aspects of physicians’ professional culture may have relevance for patient safety. Expectations of being infallible reduce their willingness to talk about errors they make, thus limiting opportunities for learning from errors. Walk Rounds are perceived to contribute to increased learning concerning patient safety and could potentially have a positive influence on patient safety culture.