This chapter examines knowledge sharing between Communities of Practice, a relatively neglected topic of study. Theory and evidence is presented to suggest that knowledge sharing between communities is likely to be more complex than intra-community knowledge sharing, due to the lack of shared consensual knowledge or shared sense of identity, which typically exists in inter-community contexts. In such situations, the development of trust is seen to be a key foundation, which requires to be developed before effective knowledge sharing can occur. Three brief case studies are presented to illustrate the arguments made. Practitioner implications flowing from this chapter are twofold. Firstly, to facilitate effective inter-community knowledge sharing requires effort to be invested in developing the social relationship (and hence trust) between members from the communities. Secondly, organizations need to balance their efforts at building Communities of Practice, with supporting inter-community interactions, otherwise they risk developing isolated and inward looking communities.