The overall aim of this thesis was to investigate patient safety in the emergency department (ED) and to determine whether this varies according to patient safety culture, waiting, and outcomes of efficiency and quality variables. I: Patient safety culture was described in the EDs of two different hospitals before and after a quality improvement project. The questionnaire “Hospital Survey on Patient Safety Culture” was used to investigate the patient safety culture. The main finding was that the staff at both hospitals scored more positively in the dimension Team-work within hospital after implementing a new work model aimed at improving patient flow and patient safety in the ED. Otherwise, we found only modest improvements. II: Grounded theory was used to explore what happens in the ED from the staff perspective. Their main concern was reducing patients’ non-acceptable waiting time. Management of waiting was improved either by increasing the throughput of patient flow by structure pushing and by shuffling patients, or by changing the experience of waiting by calming patients and by feinting to cover up. III: Three Swedish EDs with different triage models were compared in terms of efficiency and quality. The median length of stay was 158 minutes for physician-led team triage compared with 243 and 197 minutes for nurse–emergency physician and nurse–junior physician triage, respectively. Quality indicators (i.e., patients leaving before treatment was completed, the rate of unscheduled return within 24 and 72 hours, and mortality rate within 7 and 30 days) improved under the physician-led team triage. IV: Efficiency and quality variables were compared from before (2008) to after (2012) a reorganization with a shift of triage model at a single ED. Time from registration to physician decreased by 47 minutes, and the length of stay decreased by 34 minutes. Several quality measures differed between the two years, in favour of 2012. Patients leaving before treatment was completed, unscheduled return within 24 and 72 hours, and mortality rate within 7 and 30 days all improved despite the reduced admission rate. In conclusion, the studies underscore the need to improve patient safety in the ED. It is important to the patient safety culture to reduce patient waiting because it dynamically affects both patients and staff. Physician-led team triage may be a suitable model for reducing patient waiting time and increasing patient safety.