The purpose of this monograph, "Sustaining Operational Maneuver in the Twenty-First Century," is to determine if the United States Army can sustain operational maneuver in the twenty-first century. The author determined that the army can sustain operational maneuver but still needs to address four areas. First, there are issues regarding the operational level logistics system (primarily command and control and command support relationships). Second, there is a lack of logistics support at the divisional level. Third, the army has an inordinate focus on short, decisive battles rather than on long campaigns. Finally, some minor issues still exist at the tactical level of logistics which the army needs to analyze. The author employed a case study method in this monograph which analyzed three operations. These campaigns involved extensive operational maneuver against an entrenched enemy who lacked air supremacy. The 1st Infantry Division was the common element in each campaign. First, the author analyzed Operation COBRA during the Normandy Campaign in 1944. Next, the author reviewed Operation DESERT STORM in 1991. Finally, the author created a notional case study--Operation GREEN DAWN--war in Iraq against Iran in 2012. The author further subdivided each case study into sections which covered the divisional or brigade structure; combat operations; strategic and operational level logistics; tactical level logistics; and the results of logistics support based around the '35MM' model (fuel, ammunition, maintenance, and medical support). The first two case studies offer historical lessons learned regarding sustaining operational maneuver. The last case study addresses how the U.S. Army would sustain operational maneuver in the near future in a realistic scenario. The author concluded by analyzing all three campaigns based on the principles of sustainment. These findings and the results of each section determined that the army can sustain operational maneuver in the twenty-first century. The author posited a list of recommendations at the operational levels of logistics. These improvements to the logistics architecture would aid the army in sustaining operational maneuver in the twenty-first century.