This book has attempted to shed light on the guarantee of fair and equitable treatment for foreign investors in international investment law. As the most general clause in international investment agreements, fair and equitable treatment is, like no other investment protection obligation, Janus-faced. On the one hand, fair and equitable treatment depicts a norm which is couched in simple and plausible words, hardly controvertible by anyone. As such, it appears to be a universally accepted standard in international investment relations. On the other hand, the vagueness of this norm triggers fervid controversies on the concrete meaning of fair and equitable treatment and causes great difficulties in its judicial application on particular factual situations. Moreover, just as Janus is considered in Roman mythology as the deity of gates, bridges and transition, fair and equitable treatment has been referred to as a gateway to other sub-systems of international law and an overarching idea of justice. In the same vein, fair and equitable treatment has been described as a bridge between seemingly conflicting conceptions of investment protection and the sovereignty of states – the transition between stability and change.

However, unlike the figure of Janus, the concept of fair and equitable treatment neither emanates from an ancient legend nor from a mythical intrinsic meaning of its words, but is rather a man-made construction of arbitrators dealing with this norm.