TG is often subject to high-voltage politics. Yet, it is not entirely immune from normativity. This book showed that the impact of international law is increasingly being felt in the field of TG, and furthermore suggested that TG norms and practices are, conversely, enriching international law, even if only modestly by adding non-negligible detail to some of its pre-existing fundamental principles. The current emergence of customary rules in relation to TG, testified by a perusal of practice, does not itself happen in a normative vacuum.