Contractors are big business and a big part of war, with businesses taking upon themselves many tasks previously designated to the armed forces. By 2007, there were over 100,000 individuals working on U.S. contracts in Iraq and Afghanistan-versus about 160,000 U.S. combat troops. By some estimates, contractors account for some 40 percent of the costs of running operations.

This important work examines how that came to be, as well as answering a number of critical questions: How have Congress, public interest groups, and other parties dealt with the issue? How is the marketplace...