This chapter presents the research question, the arguments of the book, the contribution to the literature, the data consulted, and the methodology employed. The research question of the book is the following: how and why did EU fiscal regulation change from its beginning (Maastricht Treaty, 1992) until 2025—the time after the 2024 reform of the Stability and Growth Pact (SGP)? The book starts with two arguments: firstly, the EU’s fiscal regulation paradigm has not only changed in terms of instruments and settings, but also regarding the underlying fiscal ideas, propositions suggesting a certain approach to the content, the scope of application, and the enforcement of EU fiscal rules. Examples of fiscal ideas are flexibility and differentiation. The seven phases of EU fiscal regulation (establishing, securing, strengthening, questioning, suspending, reforming, and overcoming) have witnessed different combinations of fiscal ideas and related policy instruments, but not a truly paradigmatic change. Secondly, this ideational change has been the result of a constant compromise between competing fiscal ideas supported by the two key veto players, Germany and France. The book adopts thematic analysis of relevant EU fiscal legislation and—to explain the agreement on the 2024 reform of the SGP—process tracing.