The Combat Studies Institute is pleased to present Scouts Out The Development of Reconnaissance Units in Modern Armies by CSI historian John J. McGrath. Scouts Out is a wide-ranging historical survey of the theory, doctrine, organization, and employment of reconnaissance units since the era of mechanization in the early 20th century. Reconnaissance and counterreconnaissance are battlefield missions as old as military history itself and missions for which many armies have created specialized units to perform. In most cases, these units were trained, equipped, and used differently from the majority of an army's fighting units. Horse cavalry performed these missions for centuries, for it had speed and mobility far in excess of main battle units. Once the horse was replaced by mechanization, however, the mobility advantage once enjoyed by the horse cavalry disappeared. Since the early 20th century, the search for the proper mix of equipment, the proper organization, and the proper employment of reconnaissance units has bedeviled armies around the world. This survey uses a diverse variety of historical cases to illustrate the enduring issues that surround the equipping, organizing, and employment of reconnaissance units. It seems that these specialized units are either too heavily or too lightly equipped and too narrowly specialized or too conventionally organized. Prewar reconnaissance doctrines tend to undergo significant change once fighting begins, leading to postconflict analysis that reconnaissance units were "misused" in one way or another. McGrath ends his study with an intriguing conclusion about the role that specialized reconnaissance units should have in the future that may surprise many readers. Scouts Out is a thought-provoking historical study that we believe will contribute to the Army's current and future transformation efforts.