One of the most important questions that must be tackled in defining a benchmark of accountability is to identify its purpose, objective or rationale. The first challenge is to identify the underlying purpose or rationale for accountability. After all, we cannot hope to say whether an amount of accountability is ‘ideal’ unless we can indicate what an ideal status quo position looks like. This chapter identifies the overarching goal of accountability as being to reinforce the legitimacy of government. In a more concrete sense, that overarching goal is supported through five rationales. The first is transparency, which is concerned with providing the public with a means to scrutinise government decisions and operations. The second is control, which is concerned with providing the public with a means to ensure that the government complies with relevant requirements. The third is redress, which is concerned with providing redress to individuals harmed by government wrongdoing. The fourth is desert, which is concerned with condemning wrongdoing, and the fifth is deterrence, which is about encouraging improved processes going forward.