The Statutes of the ad hoc Tribunals grant prosecutorial staff functional immunity, which aims to protect them against undue interference by states. Defence counsel, however, is not mentioned. As a result, it is unclear if counsel enjoy any such protection, and if so, what shape or form this may take. While the ad hoc Tribunals' Statutes are silent on this matter, the arrests of defence counsel in Croatia and Rwanda have forced the ICTY and ICTR to address this omission, which has generated a body of case law that will provide the starting point for this article. The different decisions can be classified into three distinct approaches, which will accordingly be scrutinized. This article will advocate a principled approach to defence counsel immunity, consisting of functional and personal immunity, as well as a principled approach to the waiver thereof. This will both ensure the necessary protection of an effective defence, while preventing these immunity arrangements to result in impunity.