Since the start of the twenty-first century, military contractors such as Blackwater (now named Academi), Kellogg, Brown & Root, and SNC Lavalin have become household names in many countries. The reasons for their prominence vary from case to case. One is notoriety. Particular firms hold contracts valued in the millions if not billions of dollars, and the conduct of some firms has not been beyond reproach in terms of military effectiveness or their observance of human rights. A second reason is reliance. Contractors are needed to keep state military personnel fed and supplied, to maintain their machines, and in some cases even to protect them. Developed world states especially require them for warring, training, and simply operating given the limited numbers of available national military personnel, the increasing sophistication of military technologies, and the political ramifications of applying state forces overseas. In many states, contractors have therefore become part of the total national force. Yet another reason pertains to dedication and sacrifice. Many firms suffered significant levels of casualties during the longterm interventions in Iraq and Afghanistan. Thousands of contracted personnel have provided continuity over the long haul in often austere and intemperate conditions. All of this points to the considerable depth and scope of contractor involvement, arguably unprecedented in recent decades if not centuries. It also stands at odds with traditional conceptions of expensive state security sectors and their capabilities and responsibilities to manage and apply violence.Without a doubt, then, contractors have played a significant, augmentative, and sometimes controversial role in the overseas endeavours of many countries. With the first decade of this century now over and the interventions it hosted gradually fading into history, it is appropriate to consider, both by casting back and by looking forward, the evolving relationships between states and contractors. While there have been common pressures applied against contractor-employing states (especially related to the lure of neoliberal policies and the distinction between offensive and defensive violence), the national management of, and response to, those pressures have differed. Therefore, the following articles examine evolving national considerations and rationales for military contracting (including armed and unarmed contractors) based on recent experiences of selected Western states: the United Kingdom, the United States, Canada, and Sweden. Among the national cases, the United Kingdom and the United States are presented first since these countries' interactions with the private sector are arguably the most substantial in a global sense. They are also the states on which other states often model their interactions with contractors. In contrast, Canada and Sweden are examined less frequently. They too, however, present their own unique dynamics. Canada often attempts to punch above its weight on the international stage despite (or because of) its military's relatively small size. Swedish defence policy is shifting its emphasis from territorial defence and national service to expeditionary operations with professional volunteer forces. To facilitate these states' efforts, policymakers have introduced contractors in a variety of ways.The reader will note that not only does this introduction employ the fairly malleable word contractor, but that the articles that follow use a number of different terms with several meanings. This catholic approach highlights debates within the field. But, keeping International Journal's audience in mind, the terminology also reflects the varying emphasis in the broad industry on teeth aspects-those more closely associated with the use of force-and tail aspects-those more closely associated with logistics, maintenance, and support. The variance also underscores the definitions laid out in national and international regulations and guidelines. …