This article focuses on the fact that there is a noticeable difference in the way private security companies are used in Iraqi security sector reform (SSR) between the U.S. and U.K. militaries, and argues that such difference results from the two countries' different historical experiences in counterinsurgency after World War II and that, as a result of the different experiences, each military has fostered contrasting recognition toward legitimacy. The argument in this article can contribute to studies of relationship between norms and policy-making.