The Kimberley Process Certification Scheme (KPCS) aims to prevent so-called conflict diamonds – diamonds that come from conflict zones – from entering world markets. The scheme works by tracking diamonds and by limiting trade among KPCS members to certified diamonds. This paper studies the scheme’s impact on armed conflict in Africa. We exploit grid-cell level variation in the propensity to extract alluvial diamonds, and compare grid cells with and without this propensity before and after the introduction of the KPCS in 2002. Our results show that the KPCS led to a permanent and significant reduction in armed conflict.