This chapter examines the regulatory frameworks and policies that form the foundational “Rulebook” layer of the Sustainable Finance Operating System. It establishes regulation as essential for market stability, transparency, and directing capital toward sustainability goals. The chapter outlines the primary policy levers available: (1) altering the economics of sustainability through mechanisms like carbon pricing and incentives and (2) redirecting capital flows by mandating standardized information disclosure and classification systems. Focusing on the European Union as a key example of a comprehensive rules-based approach, the chapter details its regulatory architecture and the interconnected roles of the EU Taxonomy, the Corporate Sustainability Reporting Directive (CSRD) and the Sustainable Finance Disclosure Regulation (SFDR). It also explores the increasing role of central banks in monitoring climate-related systemic risks and integrating these into financial stability mandates. Finally, the chapter discusses the critical function of public incentives in steering investment.