Ensuring that nurses and other health care professionals practice in environments that enable the delivery of safe care is a challenge for today's nurse leaders. This research explores the ways in which the critical care practice environment contributes to, or prevents, the delivery of safe patient care. This study is unique in that it explores the perceptions of multiple direct care providers (e.g. nurses, physicians, other health professionals) simultaneously, as a means of maximizing knowledge about critical care teamwork and the role nurse leaders play in creating quality professional practice environments that support the delivery of safe care. Focus groups data (N=32) was collected from direct care providers (N=197) in 6 critical care units in Ontario, between September 2005 to March, 2006.  Qualitative methods are used to explore the meaning and human interactions associated with patient safety and interprofessional teamwork within the context of the critical care setting.  Feedback indicates that critical care providers are primarily concerned about threats related to standards of practice, nursing and medical staff competencies, and poor communication and teamwork. The results suggest that, while expert nurses play a critical role in creating conditions of safety for patients, there is an uncomfortable tension between threats that are linked to provider knowledge and experience and those linked to workplace conditions. In the critical care culture of “controlled threat”, providers have divergent understandings of the limits of safe performance which influences their ability to consistently defend against potential errors and accidents. Implications for improved patient safety outcomes include the development of “new” nurse leaders and “new” ways of understanding quality worklife in the critical care practice environment.