This book examines how climate change significantly impacts the public interest of national states, affecting a wide range of human rights, economic activities, development projects, and security. This book highlights the complexity of the legal discipline of climate change, which is a polycentric phenomenon because its causes and possible responses are subject to various decision-making levels and are cumulative over time. Additionally, this book addresses the need for norm creation in a scenario of risk and scientific uncertainty, as well as the socio-political conflicts generated. Given these factors, this book emphasizes the role of national states in the legal regulation of climate change, as, although it is a global problem, they are the ones who set emission reduction targets and regulate the behavior of individuals and corporations to achieve them. In recent years, various climate laws have been created or amended in several countries, indicating a push for juridification around the issue. Considering this context, this book argues that the legal discipline of climate change in Brazilian law requires the legislative structuring of a national policy compatible with the constitutional foundations and international commitments undertaken by Brazil, capable of dealing with the problem in a crosscutting manner and covering various economic sectors. This book analyzes the bases for formulating this climate policy, consisting of the foundations that should underpin it. Firstly, this book highlights that the justice aspects involved are relevant to guide the definitions of the distribution of the impacts of climate change and the measures to mitigate them. Secondly, this book addresses the protection of fundamental rights to which the state is bound, creating a duty for it to structure measures to make them effective – including regulating the behavior of individuals and corporations – and enabling judicial control in the event of violations of these duties. Lastly, this book emphasizes that the principles of environmental law must underpin the instruments of a climate policy and the interpretation of its rules.