Europe’s fiscal debates usually revolve around efficiency and growth, but rarely about democratic legitimacy. Let’s Agree on Poland: A Case Study of Constitutional Design (Oxford University Press, 2025), the product of a remarkable collective effort by 130 progressive and conservative Polish intellectuals, breaks new ground by proposing the full regionalization of income taxation — a bold aspirational proposal that has already inspired reforms in local government financing introduced by the Tusk government. While acknowledging those reforms as a step in the right direction, the book argues for adopting the “full package.” It presents detailed calculations and simulations showing how devolving income tax revenues could give regions genuine responsibility and ownership while reducing polarization at the national level. This policy-oriented seminar will connect Poland’s radical blueprint to European debates on fiscal federalism and subsidiarity, testing whether taxation can serve as a constitutional tool for trust-building as well as a financial one.