The relationship between international law on reparations and jus cogens is an uneasy one. The law on reparations is a settled part of classical international law, with roots so deep that its place in international law is taken for granted.1 The oft-quoted dictum in the 1928 Chorzów Factory case which sets out the requirement for reparation to “as far as possible, wipe out all the consequences of [an] illegal act and re-establish the situation” which would have existed but for the unlawful act was said, at the time, to be based on “international practice and … decisions of arbitral tribunals.”2 The same is not true of jus cogens, a relatively new entrant to the mainstream of international law, whose pedigree in the system is less assured, and whose application, as opposed to mere references, by international courts is almost non-existent.3 Yet, at the same time, at the heart of both reparations and jus cogens, is the notion of justice. The idea of undoing the effects of a wrongful act is intrinsically about (re)balancing the scales, while the notion of jus cogens seeks to infuse the system of international law with community values and a spirit of justice.