Study objective: We identify and describe emergency physicians' and nurses' perceptions of the effect of an integrated emergency department (ED) information system on the quality of care delivered in the ED. Methods: A qualitative study was conducted in 4 urban EDs, with each site using the same ED information system. Participants (n=97) were physicians and nurses with data collected by 69 detailed interviews, 5 focus groups (28 participants), and 26 hours of structured observations. Results: Results revealed new perspectives on how an integrated ED information system was perceived to affect incentives for use, awareness of colleagues' activities, and workflow. A key incentive was related to the positive effect of the ED information system on clinical decisionmaking because of improved and quicker access to patient-specific and knowledge-base information compared with the previous stand-alone ED information system. Synchronous access to patient data was perceived to lead to enhanced awareness by individual physicians and nurses of what others were doing within and outside the ED, which participants claimed contributed to improved care coordination, communication, clinical documentation, and the consultation process. There was difficulty incorporating the use of the ED information system with clinicians' work, particularly in relation to increased task complexity; duplicate documentation, and computer issues related to system usability, hardware, and individuals' computer skills and knowledge. Conclusion: Physicians and nurses perceived that the integrated ED information system contributed to improvements in the delivery of patient care, enabling faster and better-informed decisionmaking and specialty consultations. The challenge of electronic clinical documentation and balancing data entry demands with system benefits necessitates that new methods of data capture, suited to busy clinical environments, be developed.