Over the last decade, international investment law has become an increasingly relevant discipline. To some extent, the law’s rise to prominence merely follows factual developments, namely the increased importance of foreign direct investment. Yet another factor would seem to be equally important: International law has accepted an increasingly broad notion of ‘investment’, and thereby included a heterogeneous range of economic transactions into the area of investment law and within the potential jurisdiction of investment tribunals. The study under review, a doctoral dissertation submitted by Jan-Frederik Belling, analyses this latter factor, and in so doing, helps us appreciate the surprising rise to prominence of a niche area of law whose future, a generation ago, seemed at best uncertain.