The article discusses the application of one particular tool international criminal tribunals may use in order to bolster their perceived legitimacy: consistent resort to domestic criminal law (DCL). Arguably, legitimacy concerns affect decisions by tribunals to invoke DCL, as well as the manner in which DCL is applied. After presenting a general analysis of the pros and cons of the utilization of DCL from a legitimacy perspective (a discussion informed by some of the literature on comparative law), and after introducing a typology of possible uses of DCL by international criminal tribunals, the article explores three case studies involving reliance on DCL or lack thereof: (1) The invocation of a common plan or conspiracy by the Nuremberg Tribunal and the subsequent treatment of the Joint Criminal Enterprise doctrine by the International Criminal Tribunal for the former Yugoslavia (ICTY), the International Criminal Tribunal for Rwanda (ICTR), the Extraordinary Chambers in the Courts of Cambodia and the International Criminal Court; (2) the incorporation of domestic sentencing standards in the case law of ICTY and ICTR; and (3) the decision by the Special Court for Sierra Leone not to utilize in its work domestic Sierra Leone criminal law (notwithstanding the authorization found in its Statute). Through a discussion of these cases, I try to speculate upon the tribunals' motivations in employing DCL in the first place, and in selecting between different sources of DCL (particularly, in choosing the countries whose laws are to be consulted). On the basis of this discussion, I will attempt to map the different functions which the invocation of DCL may fulfil in the work of international criminal tribunals.