An important potential contribution to the efficient use of the health workforce, is the possibility of "skill mix" changes. "Skill mix" is a relatively broad term which can refer to the mix of staff in the workforce or the demarcation of roles and activities among different categories of staff. Most of the policy attention on using skill-mix changes to improve health system performance has been on the mix between physicians and nurses. Skill-mix changes may involve a variety of developments including enhancement of skills among a particular group of staff, substitution between different groups, delegation up and down a uni-discipliniary ladder, and innovation in roles. Such changes may be driven by a variety of motives including service innovation, shortages of particular categories of worker (especially in inner cities or rural areas), quality improvement, and a desire to improve the cost- effectiveness of service delivery. There are large differences in reported physician/nurse ratios across OECD countries and evidence of significant changes over time in some countries. This raises the issue of the direction of change and its desirability. This report examines skill-mix changes between physicians and nurses both in primary care and in the hospital setting. The report has three components: (1) literature review; (2) assessment of country returns to an OECD survey; and (3) detailed country case studies, on England and the United States. (Country Case Studies and Questionnaire are annexed. Contains 4 footnotes, 1 figure and 9 tables.)