Ninety per cent of international courts’ (ICs) legal decisions have been issued within the last two decades. This increase in case law - along with other significant changes in the operation of ICs - signals a new form of judicialised international law. This change is best described as a shift from a 'static' regime of contractual relations between sovereign states to a more 'organic' regime of 'living law'. In criminal law, this development is exemplified by the reasoning of the ICTY, the ICTR and the ICC. In examining the institutional undercurrents that accompany these changes important questions arise: through what social processes is legitimacy imputed to ICs? How do ICs handle or avoid crises in legitimacy? In the context of recent critiques of judicial reasoning in international criminal law, the article suggests that the analysis of case law from ICs must become as dynamic and agile as contemporary international law itself.