When trying to measure fiscal decentralisation, the OECD Network on Fiscal Relations Across Government Levels has made significant progress in the last years, especially on tax autonomy of sub-central governments. But in many respects, real-world fiscal decentralisation still escapes the measuring tools, especially when it comes to measure the spending power of sub-central governments or the various regulations attached to intergovernmental grants. This book deals with two interrelated issues. The first concerns  the various measurement of fiscal decentralization in general and their usefulness for policy analysis. The second and more specific issue concerns the taxonomy of intergovernmental grants and the  limits of the current classifications, and how policy changes to the intergovernmental grants framework may require that measurement devices be adapted.