Leaders of anti-corruption agencies frequently encounter opposition from powerful beneficiaries of existing corruption. Those antagonists often seek to neutralize the agencies by weakening the agencies’ credibility, legal power, or operations. Drawing from ISS interviews and case studies, this cross-cutting report explores responses to this strategic challenge by agencies in eight countries (Botswana, Croatia, Ghana, Indonesia, Latvia, Lithuania, Mauritius, and Slovenia). The leaders and staff of those agencies worked to overcome opposition by recruiting allies, instituting internal controls to bolster transparency and accountability, pursuing low-visibility preventive efforts, and carefully assessing the pros and cons of high-level investigations. The outcomes of their efforts point to conditions that shape effectiveness and suggest possible workarounds or alternative approaches for anti-corruption agencies in adverse circumstances.