The staff of the Army of the Potomac serves as the best example of the adaptive transformation of capabilities out of necessity and experience. It developed systems similar to an operations process, organic intelligence processing capabilities, and advised the commanding general whose span of control and operational reach surpassed the capacity of his mental genius. Staff processes evolved because of the decentralization of responsibilities to staff departments and away from the commander. Accurate assessment of enemy and friendly combat power were critical to battle planning, including long distance logistics operations. Understanding how the general staff developed its capabilities and processes provides insight into how the Army of the Potomac was able to defeat large-scale armies while conducting simultaneous operations. This monograph examines the significant impact of the staff on commanders as operational artists, how commanders utilize their staffs, leverage staff products and analysis, and support their planning to achieve their strategic objectives. Three qualitative case studies explore the composition and capabilities of the Army of the Potomac during three distinct periods during the American Civil War and assess staff effectiveness, its impact on the commander's decision-making process, and activities during combat operations.