[Excerpt from authors] There is a global nursing shortage. Few health services decision makers have made the critical link between the number of human resources, the characteristics of the work environment and the impact on patients, nurses, and the system as a whole. The purpose of this article is to review evidence about nurse workload, staffing, skill mix, turnover, and organizational characteristics' effect on outcomes; discuss methodological considerations in this research; discuss research initiatives currently under way; review policy initiatives in different countries; and make recommendations where more research is needed. Overall, an understanding of the relationships among nurse staffing and organizational climate to patient safety and health outcomes is beginning to emerge in the literature. Little is known about nursing turnover and more evidence is needed with consistent definitions and control of underlying patient characteristics. Research and policy initiatives in Australia, Canada, New Zealand, and the United States are summarized.