Enterprise Systems (ESs) are more than a collection of people, technology, processes, and capabilities. The responsibilities of post implementation management of ES lie in the unit called the Competency Center (CC). The CC has a bidirectional relationship with ESs wherein the CC influences the shaping of ESs, and the CC is affected by the dynamic interaction between people, technology, process, and capabilities within the ES. These dynamic interactions keep the CC, fluid and always in-process. The general-use definition of the term “process” as used in the Enterprise Systems literature treats the notion as “repeatable processes” or "replicable processes". However, arising from comparative case studies in four large organizations, I found that decision making, managing, and governing in the ES are not “replicable processes”, not reifications of structural variations over time when examined through the lens of the Assemblage Theory. Assemblage Theory incorporates the dynamic interplay of two continua: the first, territorialization, deterritorialization, and reterritorialization, and the second, material vs. expression. Although the notion of the terms formation, deformation, and reformation are suitable for understanding the processes these CCs encounter in a broad and general manner, they do not sufficiently describe the not-so-solid, never-quite-finished, always in-process or structuring referred to by Hopper (1996) as "emergent regularities". In contrast to the notion of stable structures, this dissertation research adopts the language of Deleuzian assemblage of Territorialization, deterritorialization, and Reterritorialization. Although the four study organizations planned and intended to develop clearly defined competency centers, which would create formalized processes and procedures to manage the post implementation phase, none of the study organizations ever achieved the anticipated stability. Instead, the CCs exhibited the signs of being ‘in-process’ and ‘structuring’. The contribution of this research to the IS field is an understanding of the CCs as processes as opposed to structures and how CCs structuring impact the ESs in organizations.