John Singleton Mosby led a successful partisan campaign during the American Civil War for the Confederacy. Prior to the war, Mosby was a frail nondescript lawyer. Entering the war as a private; Mosby eventually rose to the rank of Colonel. He organized, trained, and equipped the 43rd Virginia Cavalry, better known as Mosby’s Rangers. This unit grew from nine men to almost nine hundred at the war’s end, and conducted many daring celebrated raids on the Union forces and their supply lines. In addition to his raids Mosby provided accurate and timely intelligence to Major General J. E. B. Stuart and General Robert E. Lee throughout his service. This study is a leadership analysis of John Singleton Mosby using the U.S. Army’s Field Manual 22-1 00, Army Leadership. The study examines Mosby’s leadership development and evaluates him against the sixteen leadership dimensions that the Army currently uses to evaluate potential officers. The purpose of this study is to determine what leadership qualities Mosby possessed that contributed to his success. The study concludes that Mosby was able to influence subordinates, peers, superiors, and noncombatants; he provided a purpose and gave them direction and motivation; he also continuously sought ways to improve and expand the organization.