This book shows how the links between energy security and national and international law and policies on green energy pose challenges to a transition towards a green energy system. Based on empirical work carried out in two very different country case studies - Great Britain and Brazil - this book attempts to foster a better understanding of the role played by energy security in constructing and deconstructing green energy policy initiatives. The broad range of views raised in national contexts leads to legal disputes in international forums when attempts are made to address the issues of this energy security/green energy interplay. As such, building on the findings of the case studies, this book then analyses the interplay between energy security and green energy development in international trade law as encapsulated in the law of the World Trade Organisation (WTO). Finally, the author proposes a way forward in creating the legal space in the law of the WTO for trade restrictive measures aimed at ensuring green energy security.