Accountability is often referred to as an essential feature of modern democratic society, said to underpin the legitimacy of government. In this context, it is common to hear claims of accountability ‘deficit’ (ie that a particular mechanism or area is lacking in accountability) and ‘overload’ (ie that a particular mechanism or area over-delivers on accountability). Despite the frequency of references to these concepts, their precise content remains undeveloped. This book offers an explanation of the concepts of accountability deficit and overload, as well as a framework for future discussion and exploration of these ideas. It outlines the scale of the challenges of defining an accountability benchmark and developing a picture of accountability mechanisms as a system. While difficult, if accountability is indeed a foundational concept underpinning our system of government, there is merit in meeting these challenges head-on.