Legal interpretation is pivotal to a substantial proportion of the day-to-day practices at the ICC. From legal staff working at the ICC’s Judicial Divisions to defense counsel, much of the daily work at the ICC consists of conducting legal research and assessing the applicability of legal provisions to the specific case at hand. Researching interpretive practices – and the interpretive communities in which these practices are enacted – is therefore key to opening up the ‘black box’ of the ICC. Despite their centrality, getting a glimpse behind the scenes of legal interpretation at international courts is notoriously difficult, not least because of the secrecy of judicial deliberations. Drawing on practice theory, this paper a) suggests using the parallel concepts of communities of practice and interpretive communities as a conceptual lens to research interpretive legal practices; and b) outlines a methodological toolbox for researching such practices empirically. To illustrate the types of insights that these different options offer, the chapter analyzes how judges and legal staff at the ICC’s Judicial Divisions refer to previous decisions of the ICTY and the ICTR in their interpretive practices. Drawing on interviews with ICC judges and legal officers and an analysis of practitioner’s handbooks, the chapter thereby explores how professional assumptions shared by international lawyers on, for example, the interpretive weight attributed to the jurisprudence of the ad hoc Tribunals are themselves subject to contestation.