Climate change, it is often said, is the greatest challenge of our time. As a global phenomenon with a long temporal reach, the impacts of climate change amplify challenges already faced across social, political, economic and ecological spheres. Similarly, constitutional theory is not immune from the impacts of climate change. Yet scholarly engagements between constitutional theory and climate change have thus far been targeted and disparate. This chapter represents an attempt to face up to the challenge of climate change from the perspective of constitutional theory. It takes seriously the discourse of “climate emergency” to argue that emergency is a theoretically defensible framing of the problem. Using the rule of law, rights and federalism as three examples of the challenges that climate change poses for constitutional theory, it highlights some strengths and limitations of existing literatures on these three concepts. Ultimately, it shows that the climate emergency points us to a theory of constitutionalism that builds on these strengths, responds to these limits and provides a path forward for thinking through the role of constitutional theory in a climate-disrupted world.