Persecution has found contemporary acceptance as conduct constituting one of the enumerated inhumane acts of crimes against humanity in terms of the Rome Statute of the International Criminal Court (ICC). Despite its proscription under international criminal law, religious discrimination and religion-based persecution remain a major human rights issue of national and international concern. Accordingly, international prosecution systems are to be resorted to in pursuit of criminal accountability. However, the incessant impunity for persecution is not due to the lack of proscription in international law, but stems rather from definitional instability and legal vagueness, which is consequently addressed in this dissertation. The paper proposes a justifiable, comprehensively formulated and pragmatically verified conceptualisation of "Ë−grievous religious persecution' as a crime against humanity. In this regard, a relevant taxonomy is proposed which differentiates between different forms of persecutory conduct, discusses the mens rea requirement, establishes the intensity threshold, recommends an effective definition, and is finally applied to a relevant case study in order to analyse its practical efficiency. In furtherance thereof, the writer takes a multidisciplinary approach, briefly examining the existential nature of religious identity and freedom, as well as its role in characterising persecution as religion-orientated. This conceptualisation advances the legal discourse relating to religious persecution, which may potentially lessen the political and judicial unease regarding its perceived scope and application. This strengthens the efforts of human rights defenders, advances criminal accountability and counteracts impunity for "Ë−grievous religious persecution'. The overall thesis is therefore that it is possible to convincingly conceptualise "Ë−grievous religious persecution' by denoting a definitively formulated and pragmatically verified taxonomy of the legal preconditions for establishing the ICC's subject-matter jurisdiction.