Recent assertions have been made that the nature of warfare in our current operating environment has changed in such a way that phasing in military operations has outlasted its utility and become problematic, requiring it to be eliminated or replaced in military planning. The problem this monograph attempts to evaluate and solve is whether or not phasing in U.S. Military doctrine and operational design still has utility in planning military operations, or if it should be eliminated or replaced by some other means of visualizing plans and arranging forces for military operations. Phasing has been utilized to assist U.S. Military commanders and planners to visualize plans and how forces should be arranged to conduct military operations and campaigns since the creation of operational design in the 1920's. Phasing has been applied in planning conventional as well as non-conventional military operations. Recent criticisms of phasing have surfaced in the aftermath of Operation Iraqi Freedom's failure to rapidly stabilize Iraq in Phase IV of the operation. This paper analyzes phasing through theoretical and historical influences to trace how it has become a part of operational design and planning. Phasing is described and defined in U.S. Military doctrine from its first appearance as a method to assist in planning in the 1920's to the present and historical examples are provided as examples of its use. Mao Tse Tung's use of phasing to visualize the strategy for conducting his Protracted War against Japan is analyzed to determine what influence it may have had on U.S. Military doctrine. Criticism of phasing and proposed alternatives are presented and scrutinized through Systems Theory, Complexity Theory, logic, and doctrine to evaluate the rationality for criticism and applicability of alternative methods for visualizing plans and arranging forces. Recent changes and modifications to phasing in U.S. Military doctrine are analyzed to understand the logic behind the changes.