This unique monograph is a concise account of the evolution of Marine Corps staff organization is derived from official records and appropriate published historical works. It is published as a ready reference for those interested in the historical development of our modern Marine Corps staff organization and, in particular, the evolution of the staff at Headquarters Marine Corps. The final responsibility for the service of a command rests with its commander. If an organization is small and the scope of its activities limited, the commander can usually direct his organization and administer its affairs personally, with, perhaps, some routine clerical assistance. In the case of a larger military organization with a considerable range of functions, the commander brings together a group of people to provide him with evaluated information and recommendations for the best courses of action to follow. As the Marine Corps has grown in numbers in order to fulfill an increasing range and scope of responsibilities, the Commandant and his subordinate commanders have followed this latter thesis. When the Corps numbered less than 1,000 officers and enlisted men, it was possible for the Commandant, with but minimum assistance, to personally direct and administer its activities. Through the years, as the strength of the Marine Corps expanded to today's 240,000 men and women, it has been necessary that the staff assistance to the Commandant be correspondingly increased to help him direct and administer the Marine Corps in its world-wide responsibilities. This account of the evolution of Marine Corps staff organization, with emphasis on the development of the Headquarters staff, is published to show why and how the Marine Corps staff has grown from its 1798 infancy to its maturity of today.