Abstract: The purpose of this study was to explore organizational forgetting processes in an organization after acquisition. The different causes of forgetting, the organizational considerations that prevent knowledge from being stored, and why some new knowledge is integrated while some is not still remain uncharted. Understanding the phenomenon of forgetting in the context of acquisitions is also important, since acquisitions continue to be a popular growth strategy despite their high rate of failure. Specifically, between 2004 and 2015, the value of acquisitions globally grew from $1.9 trillion to almost $5 trillion, yet 50% to 80% of all acquisitions fail and performance after acquisition is varied at best. A qualitative single site case study was conducted of an acquired organization’s human resources (HR) department in the pharmaceutical industry. One or two semistructured interviews were conducted with seven HR department staff, including the vice president of HR, HR managers involved in or overseeing HR routines, and other HR administrative staff. In addition, archival sources relating to a change in a routine or process were reviewed. Data were entered into Atlas.ti and coded. The focus was on organizational routines as a type of organizational knowledge. The variation, selection, and retention of new practices and patterns of actions within routines occurring on a daily basis within organizations allow for a wide range of outcomes and the impact of the process of organizational forgetting. Four primary findings emerged from this study: social and personal power influenced organizational forgetting; employees from the acquired organization were required to unlearn aspects of their pre-acquisition performance management and evaluation routines; the frequency of routines impacted organizational forgetting; and enterprise-wide technology changes, such as implementation of a new software program, were key in unlearning. Theoretical contributions to the organizational forgetting literature included clarification and greater articulation of the four modes of forgetting and the relationship between the modes. Conclusions and implications for practice are discussed, including ideas on how to manage the organizational forgetting processes to potentially increase the success of an acquisition.