The book ends with two conclusions: First, Member State fiscal sovereignty is a permanent constitutional constraint upon the application of fiscal federalism theory in the European Union. Second, hard budget constraints and market discipline are indispensable for the guiding principles of price stability and fiscal discipline in a decentralised federation bound by the fiscal sovereignty of its Member States. In sum, the model chosen for European fiscal federalism must preserve the fiscal sovereignty of its constitutional democracies, and it must have market discipline under hard budget constraints. As for the selection of an appropriate model for EU fiscal federalism, this book proposes that three constitutional tests for fiscal sovereignty identified in Chapter 1, and the five determinates of fiscal discipline identified in Chapter 8, provide an intersecting set of criteria for determining which models of fiscal federalism are compatible and implementable within the boundaries of the European legal order.