Few passages in the Canadian Constitution have generated as much debate over the years as the opening words of section 91 of the Constitution Act, 1867 commonly known as the Peace, Order, and Good Government (hereinafter “POGG”) clause. Most of the controversy about POGG centers around how to interpret the clause in a way that allows the federal government to address issues of genuine national concern (that warrant a national response) while respecting provincial autonomy and diversity in our federation. The tensions underpinning POGG were recently revealed in the trio of provincial challenges to the constitutionality of Parliament’s Greenhouse Gas Pollution Pricing Act (GGPPA), in which provinces argued that upholding the GGPPA would have the effect of displacing provincial jurisdiction over GHG emissions. While two of the three Courts of Appeal (Saskatchewan and Ontario) upheld the GGPPA as a matter of national concern under POGG, doing so was apparently a struggle, as they strained against the watertight confines of earlier eras of constitutional interpretation still evident in POGG jurisprudence. Now under appeal to the Supreme Court, this trio of references offers an opportunity for the Court to clarify the contours of POGG in the modern context of flexible, cooperative federalism. In this article, we examine three central tensions that the GGPPA appeals revealed about POGG. First, we consider, and reject, the argument that POGG benefits from a special kind of exclusivity, different from enumerated powers, that has the effect of displacing provincial power. We show that this argument is steeped in the bygone era of watertight compartments and a suggestion that POGG creates an unassailable core, akin to that which underpins the doctrine of interjurisdictional immunity. We explain why this argument is unfounded in the modern era of cooperative federalism. Second, we examine a source of confusion in the GGPPA appeals related to how the word ‘matter’ is used, which we submit contributed to the challenging provinces’ fear that provincial power will be permanent displaced if the legislation is upheld under POGG. Specifically, the challenging provinces argued that upholding the GGPPA would necessarily create a new sub-head of exclusive federal power over a broad subject matter (GHG emissions) that would displace their jurisdiction. We discuss how the word ‘matter’ is used to refer both to the pith and substance of legislation and the possibility of a new sub-head of power that could be recognized for Parliament if the law is upheld. We submit that this terminological confusion fuels the fears about the impact of upholding the legislation under POGG on provinces. Third, and most importantly, we consider the extent to which federal jurisdiction under POGG can peacefully co-exist with related provincial authority. The provincial appeals have revealed that most of the justices – even those that upheld the GGPPA – are operating under an assumption that the double aspect doctrine does not apply to matters justified under POGG. We examine the historical development of the double aspect doctrine to show that there is no basis for this assumption, and suggest the Supreme Court should clarify that the doctrine applies to matters upheld under POGG, just as it would for enumerated powers. We also argue in this paper that the Supreme Court should update the test set out in Crown Zellerbach more than 30 years ago. In the intervening decades, the courts have more fully embraced a flexible interpretation of the division of powers that tolerates more de facto concurrent operation of statutes on similar subject matters. The provincial challenges have revealed the extent to which the Crown Zellerbach test, and specifically the way in which the potential scale of impact on provincial jurisdiction is evaluated, leaves much uncertainty about the level of overlap that can operate. We deconstruct the Crown Zellerbach test and propose a more flexible, nuanced, analytical approach that empowers the federation to address pressing public policy problems such as climate change in a way that respects federalism. Ultimately, the Supreme Court has an opportunity in the GGPPA appeals to interpret POGG in a way that empowers all levels of government in our federation to respond to increasingly pressing, dynamic, multi-dimensional public policy challenges, such as climate change. Our article shows that there is a role for POGG to play in enabling the federal government to be accountable for reducing the country’s overall level of emissions in accordance with international commitments while also allowing the provinces to continue legislating to reduce GHG emissions.