This article discusses the importance of the recently concluded Paris Rulebook, the extent to which it limits national discretion, instils discipline and generates ambition and accountability, and the challenges that lie ahead in implementing the 2015 Paris Agreement. It discusses, in particular, the rules on mitigation, transparency, the global stocktake and the implementation and compliance mechanism, in order to highlight the choices Parties made on three overarching issues that have long bedevilled the climate change regime—prescriptiveness (the level of detail of the rules), legal bindingness (the extent to which particular rules are legally binding) and differentiation (the extent to which particular rules accommodate differences between Parties or apply uniformly to all Parties).