This chapter will analyze the inspector general (IG) concept including why Offices of Inspector General were established, what they do, how they evolved during the last 30 years since their establishment by statute, what changed, and what influenced/challenged IGs’ effectiveness. First it addresses corruption, fraud, waste, and abuse, identifying what they involve in regard to IGs’ interventions against fraud and corruption within federal programs and operations. Second, it describes the principal activities that IGs perform in order to achieve their mission. Third, it describes the major provisions established by the Inspector General Act of 1978 and its amendments. This section analyzes main provisions related to functions of the inspector general, investigation of whistleblowing, IGs’ independence, reporting requirements, and coordination with other federal agencies. Fourth, it evaluates the major changes introduced by the Inspector General Reform Act of 2008. Finally, it addresses main issues related to components of IG effectiveness identified by the theory (e.g., recoveries, IGs’ independence versus politicization of IGs, systemic problems in hosting agency, agency implementation of IGs’ recommendations, and whistleblowing issues).