The National Crime Authority (NCA) was established to both investigate and disrupt organized criminal activity. Within the NCA, a Strategic Intelligence Unit (SIU) has been established to undertake assessments of the criminal environment and assist in prioritising areas of work for the Authority. However, there has been an enduring debate in both academic and law enforcement fields about the most appropriate conceptualisation of organized crime. The present thesis has investigated the ways in which personnel within the NCA conceptualise organized crime and apply those conceptualisations to management and investigative tasks. In particular, the definition of organized crime and the associated conceptualisation of that crime developed by the SIU has been compared with the perspectives of a range of other Authority personnel emerging from a series of 21 in-depth interviews. Analysis of the interviews reveal that while the SIU's conceptualisation of organized crime is close to that of the academic community, operational and management personnel adopt conceptualisations which arise from the specific work environments in which they operate. The thesis concludes that the needs of strategic planning, management of complex inter-agency investigations, and operational prioritisation will be better met by closer communication and co-operation between the operational and strategic areas of the Authority.