Concern about corruption has stimulated the creation of a multiplicity of indicators by a multiplicity of methods by the World Bank, World Economic Forum, Transparency International and commercial rating agencies. However, the construction of indices varies, raising substantive and methodological issues, which are reviewed with particular reference to post-Communist transition societies in Eastern Europe and Central Asia. This paper systematically examines indicators, starting with the definitional distinction between measures of administrative corruption as distinct from state capture. It pays particular attention to problems arising from the aggregation of indicators from multiple sources, and the extent to which the changing composition of cross-country indicators limits trend analysis. It concludes that many of the problems of aggregation may be avoided by using single source and single dimension indexes.