Chapter 5 discusses the ethical, political-philosophical and international-legal foundations of climate change legislation. Both climate change impacts and the mitigation of climate change affect human well-being in diverse and significant ways. Two political-philosophical frameworks – the liberal-egalitarian-inspired ‘climate justice’ framework and the utilitarian-inspired ‘economic efficiency’ framework – have dominated philosophical theorizing about how to trade-off these diverse well-being impacts in the context of climate change. International climate law borrows from both political-philosophical frameworks but ultimately constitutes a free-standing normative foundation. The chapter provides an overview and critical analysis of these various normative foundations and discusses their (limited) impact on domestic climate change legislation. It also highlights three nascent ‘movements’ at the cutting edge of climate politics and policy – anti-fossil-fuel movements, visions of green transformation, and transitional fairness/‘just transition’ claims – and discusses the alternative normative foundations on which these movements implicitly rest.