Corruption, defined as the abuse of public office for private or political gain, is an endemic feature of autocratic political systems in the Arab world. Little transparency and predatory rulers provide the ideal conditions in which graft, bribery, and extortion flourish. Corruption and authoritarianism go hand-in-hand. Yet why do so many Arab states choose to battle corruption? Since the mid-2000s, nearly a dozen Arab states have created anti-corruption agencies (ACAs). ACAs are specialized judicial bodies that investigate and prosecute corrupt deeds, and are more commonly found in democracies. Contrary to popular assumption, Arab ACAs are not paper tigers. They have substantial resources, employ capable staff, and draw international support. They do not prosecute regime heads, such as presidents, kings, and generals, but they often ensnare lesser officials and bureaucrats. That autocratic regimes would create ACAs to limit the very corruption that sustains them constitutes a major puzzle. This paper, the first study of Arab anti-corruption agencies, explains this enigma through systematic analysis of all ten Arab ACAs, which reside in Algeria, Egypt, Jordan, Kuwait, Morocco, Palestine, Qatar, Saudi Arabia, Tunisia, and the UAE. Cross-national comparisons using historical and institutional data illuminate the origins, trajectory, and results of ACA operations. Those comparisons suggest three strategic factors account for why Arab autocracies choose to selectively fight corruption. First, ACAs enable authoritarian regimes to appease Western donors and multilateral agencies like the World Bank, who may conditionalize their support upon anti-corruption reform. Second, rulers use ACAs to selectively capture public support. When street protests erupt, as in the Arab Spring, ACAs are useful: they increase their operations to prosecute more politicians, as a tactic to mollify popular frustrations over deeper economic and political problems. Third, ACAs serve as weapons for rulers to eliminate their rivals, such as party officials and business magnates. Leaders use ACAs to pursue charges of corruption, however trumped up, that sully prominent figures whose political ambitions threaten their monopoly over power. These findings leave an unexpected conclusion for future research. While ACAs are a product of strategic calculations, they are not window-dressing. They must send a credible signal for Western donors but also effectively function in order to both meet public expectations and opportunistically weaken political figures. In fulfilling these mandates, ACAs paradoxically become robust, well-run institutions – pockets of unexpected competency within otherwise bloated authoritarian systems.