The 'rural' definitions applied by the Federal Government, especially by two data-gathering agencies, the Bureau of the Census and the Office of Management and Budget (OMB), emphasize different dimensions of the concept, and delineate the rural-urban continuum in different ways. This report discusses the inconsistency of curent "rural" definitions and its impact on research data collection and health policy formation. The Census Bureau's urban-rural definitions rely on settlement size and density, while the OMB's "metropolitan statistical area" (MSA) designation more closely follows county lines. Different designations also may be used by the same program, notably for purposes of hospital classification and reimbursement under federal health programs. Some have called for the development of a standard rural typology that would capture elements of rural diversity while improving the use and comparison of nationally collected data. But a standard typology would be difficult to create, because different typologies serve different purposes. Typologies usually are based on population size and density, urbanization, relationship to an MSA, and principal economic activity. The paper concludes that better measures of population concentration would be helpful to distinguish between urban and rural areas within the same counties. (TES)