This chapter provides an in-depth account of the relationship between the U.S. intelligence apparatus and its private outriders, from the earliest days of the Republic to the end of the Cold War. Covering such a large period sheds light on the deep roots, the broad evolution, and the multiple opportunities and risks accompanying intelligence outsourcing. In the United States, the legitimacy of the federal government has always been entwined with the private sector and this is related to the values underpinning American political culture. As a result, the private intelligence industry continued to thrive, deepen and diversify its involvement in national security affairs when the federal government established itself more firmly in this realm. The institutionalization of intelligence in the twentieth century was accompanied by the diversification and formalisation of the ties between the intelligence community and its contractors. Contractors and their government sponsors share the responsibility for some of the greatest achievements and controversies in U.S. intelligence history, from the success of the U2 spy plane to the excesses of Project MKUltra. The history of U.S. intelligence is characterized by successive movements of expansion and regulation through which outsourcing and accountability have become increasingly intertwined.