A breach of fair and equitable treatment is alleged in almost every investor-state dispute. It has therefore become a controversial norm, which touches many questions at the heart of general international law. In this book, Roland Kla?ger sheds light on these controversies by exploring the deeper doctrinal foundations of fair and equitable treatment and reviewing its contentious relationship with the international minimum standard. The norm is also discussed in light of the fragmentation of international law, theories of international justice and rational balancing, and the idea of constitutionalism in international law. In this vein, a shift in the way of addressing fair and equitable treatment is proposed by focusing on the process of justificatory reasoning.