The Women, Peace and Security Agenda is unique in its kind. Built on four pillars, it is widely accepted as the main international security framework dealing with the gendered consequences on women and girls of war and violent conflict. Furthermore, it offers pathways to overcome these insecurities, promoting transformative change as a means to foster sustainable and durable peace. Having said that, the Agenda has failed to make a widespread impact on the lived experiences of women and girls on the ground. Scholars argue that this is grounded in the gap between rhetoric and implementation; while the UN, (partner-)organisations and states have expressed their support of the Agenda, various factors – among which are a one-sided and biased translation of the provisions, a lack of allocated financial and human resources, and a general lack of political commitment – suggest otherwise. This study aims to elucidate the mechanisms underlying this gap between rhetoric and implementation. One of the theoretical approaches used to research this is Feminist Institutionalism. Grounded in the New Institutionalist school, it looks both at the interactions between formal and informal institutions in driving or withstanding institutional change and the social hierarchies underlying these institutions and interactions. In line with the Agenda’s focus on positive change, this thesis will focus on the mechanisms that promote institutional change, not halt it. Grounded in the Feminist Institutionalist approach, this thesis, thus, analyses to what extent a (feminist) constellation of actors, a gendered logic of appropriateness, path dependency and the mode of incremental change are sufficient and/or necessary conditions in explaining successful implementation of the Women, Peace and Security Agenda in the Netherlands and Ireland. Using Causal-Process Tracing, this study concludes that a (feminist) constellation of actors and the level of path dependency are necessary conditions in inducing WPS-implementation. The logic of appropriateness and mode of incremental change are sufficient conditions.