The article provides an integrative framework for the diversity of research questions that are of interest to the Society of Organizational Learning (SoL) community of researchers.  Many studies on organizational learning focus on how people share knowledge in heterogeneous environments.  However, different kinds of heterogeneity pose different barriers to knowledge sharing.  The article specifies some critical boundaries that become prominent in research on organizational learning and discusses what kinds of barriers to knowledge sharing these boundaries create.  Applying the “boundary lens” results in a useful cross-pollination of ideas across diverse research streams. The article draws on the cases studies presented at the SoL Research Greenhouse on October 8^th and 9^th, 1999, in Cambridge, MA.  Integrating findings across cases studies elucidates twelve success factors that enable effective knowledge sharing across boundaries.  Also, understanding barriers to knowledge sharing shows how various leadership qualities were needed to overcome these barriers.  From methodological standpoint, it was evident that most research on this topic was conducted in collaboration with organizational participants who had practical knowledge of the context.  The article concludes by urging researchers and practitioners to examine the barriers to knowledge sharing that arise in particular contexts and to look at the trade-offs involved in applying various strategists.