Serious and organised crime is borderless and invasive, constantly seeking to identify and exploit vulnerabilities in our societies, economies, and laws. Witness protection programmes are one of the most effective means of securing convictions against otherwise untouchable senior-ranking individuals involved in organised crime. Nonetheless, such schemes, intended to circumvent the criminal code of omertà (silence), are inherently controversial, balancing a broad range of often competing rights and interests and posing significant moral hazards for the criminal justice system. Consequently, the contemporary witness protection model advocates the legitimisation of these types of schemes, underscoring the imperative to ensure accountability and transparency that conforms with the special security requirements of such programmes. This thesis represents the first study of its kind within this jurisdiction, providing a focused critical analysis of the Irish Witness Security Programme through the lens of legitimacy. A dual normative-empirical model of legitimacy is adopted which incorporates indices pertaining to accountability, transparency, democratic principles, and corruption. Moreover, within a case study research design, the methodology of this study incorporates three separate research methods, comprising a documentary review of literature on the Irish programme; a crosscomparative assessment of selected international witness protection programmes; as well as a review of the Irish programme as it operates in practice, facilitated through semi-structured interviews with key stakeholders. The findings of this study submit that the current approach to witness protection within this jurisdiction cannot be regarded as legitimate. The Irish programme represents an outlier in terms of international best practice, operating in the absence of a legislative framework. This research outlines the dangers of this perceived ‘security through obscurity’ approach adopted here, providing compelling evidence of an increased risk to the safety and well-being of witnesses, further emasculation of due process rights, as well as substantially increasing the risk of adverse practice and corruption. This thesis concludes that the current status of witness protection in Ireland emanates rather from an accepted security mindset within the state, one which frequently advocates exceptionalism in the service of state security, irrespective of outstanding legitimacy concerns.