Summary. More precise policy making at all levels of government has fuelled tremendous demand for small area data—smaller than ever before. At the same time, there has been an unprecedented accumulation of data in geographic information systems, administrative records databases and more sophisticated survey sampling schemes. Researchers and practitioners have been trying to combine these diverse sources of data. But how should these diverse sources of data be combined in a way that is policy relevant and statistically principled? The paper illustrates these questions with several example applications at the state, county and local level: emerging geographic information systems databases, the need for estimates of small area income, poverty, demographic and uninsurance data by health authorities, and how administrative records databases (such as licensed day care facilities, traffic counts and unemployment insurance records) are being harvested for their information content. Finally, the paper proposes approaches for integrating these diverse sources of data with different error, uncertainty and quality profiles, and surveys persistent challenges in this area.