This article reconstructs two periods in the process of implementation of International Humanitarian Law (IHL) by the Colombian armed forces. In the first period (1991-2006), the armed forces were alien and even hostile to both IHL and International Human Rights Law (IHRL), to the point of seeing a “judicial war” in the action of both civilian courts supervising IHL compliance and of civil society organizations that publicly denounced breaches of law. In the second period (2006-2016), the armed forces began to progressively appropriate IHL. The article reconstructs the history of this shift and shows that one of its main causes lies in the permissive and exculpatory character of IHL. Indeed, when the armed forces appealed to the legal principle of military necessity and other principles of IHL, they sought to limit the reach of civilian oversight over military operations. The article concludes by highlighting some problematic aspects of a prevalent interpretation of the relationship between IHL and IHRL as complementary and “convergent” regimes. Contrary to that interpretation, the history of IHL implementation in Colombia illustrates clearly the contrasts and differences between IHL and IHRL.