While territory, oil, andwater are frequently mentioned as resources likely to promote interstate conflict, diamonds have emerged as a prominent factor in explanations of civil war. In this article, the authors report on a new database on diamond deposits and production and analyze the relationship between diamonds and armed conflict incidence. They find a strong bivariate relationship between diamonds (particularly secondary diamonds) and the onset of civil war. Adding diamond dummies to standard models of civil war, the results are more mixed. The production of secondary diamonds increases the risk of onset of ethnic war, but not other types of war. The authors find evidence that secondary diamonds are positively related to the incidence of civil war, especially in countries divided along ethnic lines. Primary diamonds, on the other hand, make ethnic war onset and incidence less likely. The authors also find that the impact of diamonds has been substantially stronger in the post–cold war era.