This article researches the instrument of peer review among states, which is widely used by international organizations to monitor state compliance with international anticorruption norms. Despite their widespread use, little is known about the conditions under which peer reviews bear significance in the global fight against corruption. This article seeks to shed light on this by considering the authority that three major, yet hitherto understudied, peer reviews carry: the OECD Working Group on Bribery, the Council of Europe's Group of States against Corruption, and the Implementation Review Mechanism of the UN Convention against Corruption. Authority is conceptualized as a social relation between the institution carrying authority (the peer review) and the intended audience (mostly states). Drawing upon original survey data and expert interviews, the findings reveal that the three peer reviews have different degrees of authority. The article subsequently explains the observed variation in authority, by looking at the membership sizes and compositions of the peer reviews, their institutional designs, and the types of officials that are involved in the review process.