This paper critically explores ways in which knowledge is defined from a hierarchical point of view and a sociological point of view. From the sociological point of view, it suggests a new categorization of knowledge relating to knowledge flow. Then it shows how the knowledge flow approach, with this new categorization, can be a complement to existing business strategies. On the basis of previous research, barriers to effectiveness in knowledge flow are identified. A conceptual model is devised, taking account of identified barriers, to serve as a framework for developing agendas of future research aimed at the development of knowledge flow support tools.