Rational choice approaches to customary international law have gained in prominence in recent years. Although becoming increasingly sophisticated, they are not able to explain all phenomena of customary international law. This contribution claims that there are two different types of unwritten...

In their majority, public international lawyers postulate that for a new rule of customary law to originate, two conditions must be fulfilled: there must be consistent practice, and it must be shown that this practice is motivated by the belief that such behaviour is required in law. Maurice...

Customary law has been criticized from very different angles. Rational choice theorists claim that what looks like custom is nothing but self-interest. Positivists doubt that anything beyond consent assumes the force of law. In this paper, we adopt an experimental approach to test these claims....

The paper examines the potential of customary international law to protect global public goods. In particular, it focuses on the question whether customary law can contribute to the mitigation of climate change. The analysis proceeds in the three steps. First, it will have a closer look at the...

This paper examines the formation and evolution of customary international law in the field of foreign investment (Parts II and III) and its various forms interaction with international treaties, focussing mainly on BITs (Parts IV to IX). Although a comprehensive study on the customary rules for...

This contribution to a symposium on Kiobel v. Royal Dutch Petroleum Co. examines two ways of looking at the question of corporate liability under customary international law. It argues that the Second Circuit was wrong to ask whether a “norm of corporate liability” exists in the abstract and...