The aim of this article is to introduce the privatized military industry. It seeks to establish a theoretical structure in which to study the industry and explore its impact on the overall risks and dynamics of warfare. The first section discusses the emergence and global spread of PMFs, their distinguishing features, and the reasons behind the industry’s rise. The second section examines the organization and operation of this new player at the industry level of analysis (as opposed to the more common focus in the literature on individual firms). This allows the classification of the industry’s key characteristics and variation. The third section offers a series of propositions that suggest potential consequences of PMF activity for international security. It also demonstrates how critical issue areas, such as alliance patterns and civil-military relations, must be reexamined in light of the possibilities and complications that this nascent industry presents.