The paper presents an in depth study of loyalty in the military. Among the virtues a service member possesses, the author asserts that loyalty is the cornerstone for successful service. Military loyalty extends beyond commitment and trust. It necessarily traverses the boundaries of family, friendship, country, and religion by requiring the service members to subordinate themselves to a higher level of allegiance. The oath of office inspires or demands service members loyalty while the military leaders must ensure it is given. Therefore, a sound understanding of loyalty is essential to understanding its role in the profession of arms. Ten readings from various disciplines are used to explore important nuances of loyalty, such as to whom or what is it owed, its limits, how to build it, and its vices. Finally, an analysis of the common trends displays the role military loyalty plays in the profession of arms as key to successful military operations in peace and at war.