This chapter unpacks the conceptual and analytical framework of this book on accountability in EU security and defence. Accountability is first delineated as a corollary to holding (public) power and conceptualized as a three-stage mechanism. In a further step, accountability is contextualized in the particular setting of international relations, characterized by executive governance, which is the habitat of EU peacebuilding activities. The chapter then turns to accountability catalysts and inhibitors, namely institutional design, the accountability architecture, and information-sharing modes. Subsequently, the chapter offers a taxonomy of accountability in civilian CSDP by mapping actors and potential fora, both at the strategic and operational level. Prior to outlining the overall research agenda of this study, the chapter addresses analytical and practical challenges for (studying) accountability in the subject area, notably the restrictive information disclosure policy regarding EU security and defence matters.