This book traces the history of private military companies, with a special focus on UK private forces. Christopher Kinsey examines the mercenary companies that filled the ranks of many European armies right up to the 1850s, the organizations that operated in Africa in the 1960s and early 1970s, the rise of legally established private military companies in the late 1970s and early 1980s, and today's private and important actors in international security and post-conflict reconstruction. He shows how and why the change from the mercenary organizations of the 1960s and 1970s came about, as the increasing newness of private military companies came to be recognised. It then examines how PMCs have been able to impact upon international security. Finally, Kinsey looks at the type of problems and advantages that can arise for organizations that decide to use private military companies and how they can make an unique contribution to international security. Corporate Soldiers and International Security will be of great interest to all students of international politics, security studies and war studies.