One of the critical variables in the successful completion of a military campaign is the functioning of an army's command and control system. In the American Civil War, a commander's primary command and control tool was his staff. Large Civil War armies like the Army of Tennessee required significant numbers of staff personnel. Staffs existed at each level of command from regiment through the army level. Staff officers had responsibility in three broad areas: personnel and logistical support to the army, military administration, and command and control. This book analyzes the roles, functional organization, and performance of the staff of the Army of Tennessee and its subordinate corps during the Chickamauga campaign, 16 August - 22 September 1863. Primary sources for staff personnel include the Official Records of the Union and Confederate Armies, and the Compiled Service Records of staff officers. Staff performance is evaluated in terms of doctrine and practices as embodied in regulations and military literature of the day. This book concludes that, while staff performance was adequate in administration and logistical support, the performance of the command and control system was inadequate. The staff's failure in this area had a significant negative impact on the performance of the army as a whole.