This chapter reviews the literature of intelligence accountability, reviews different theories, and introduces readers to key terms such as oversight, review, control, and governance. This book complements the process of intelligence oversight—the practice of holding ISAs to account, whereby ISAs have to justify their activities—with other types and levels of accountability. Typologically, accountability bodies differ by ways and methods they use to hold ISAs accountable: they can review, oversee, or control Intelligence and Security Agencies (ISA), and/or accept and address complaints concerning actions or activities of an ISA. Although conventionally they assessed compliance within an intelligence community, as of late they have been performing additional functions, such as promoting innovation. The different types of accountability are complemented by various layers in which Intelligence and Security Agencies are held accountable: internal, managerial, and external. The chapter introduces readers to the institutional architecture of intelligence accountability: legislative committees, judicial and quasi-judicial bodies, bureaucratic and administrative bodies, and executive oversight. It goes on to review intelligence accountability frameworks: laws, legislatures, the executive, the judiciary, the media, the public, civil society, and the democratic interest. The chapter closes on developments in international and supranational accountability cooperation.