Fiscal federalism refers to the distribution of taxation and spending powers across levels of government, and is the focus of the OECD’s Network on Fiscal Relations across Levels of Government. Through decentralisation, governments can bring public services closer to households and firms, allowing for better addressing local preferences. However, unless properly designed, decentralisation can also make intergovernmental fiscal frameworks more complex and risk reinforcing interregional inequalities. This book synthesises the work of the Network over the past decade and a half, on how to balance the policy trade-offs inherent in intergovernmental fiscal relations, making use of its novel analytical results.