Throughout its history, the Department of Defense (DOD) has relied on contractors to support a wide range of military operations. Operations over the last thirty years have highlighted the critical role that contractors play in supporting U.S. troops - both in terms of the number of contractors and the type of work being performed. Over the last decade in Iraq and Afghanistan, and before that, in the Balkans, contractors accounted for 50% or more of the total military force. Regardless of whether future operations are similar to, or significantly different from, those of the past decade most analysts and defence officials believe that contractors will continue to play a central role in overseas military operations. Consequently, these observers believe that the DOD should be prepared to effectively award and manage contracts at a moment's notice, anywhere in the world, in unknown environments, and on a scale that may exceed the total contract obligations of any other federal agency. This book provides background information and identifies issues for Congress on the use of contractors to support military operations. The DOD's extensive use of contractors poses several potential policy and oversight issues for Congress and has been the focus of numerous hearings. Congress' decisions on these issues could substantially affect the extent to which the DOD relies on contractors in and is capable of planning for and overseeing contractors in future operations.