This report outlines, in broad terms, the concepts that underpin the compilation of national data on expenditure on health and welfare services in Australia, and the sources of data that are used in compiling those estimates. The AIHW is seeking to improve the general level of understanding of the different data sources used in deriving the estimates of expenditure on health and welfare services. This, in turn, could contribute to improvements in the timeliness, accuracy and relevance of the data.