In this article, the authors argue that online learning conversations need to go beyond the common "information exchange" to a deeper level of interaction in order to help learners build situated knowledge that is useful in their local contexts. The article begins by looking at the commonly-used framework of a Community of Practice (CoP) and, in particular, the challenges that designers can expect to encounter when knowledge building moves online, and conversants do not have a shared practice. The authors explain why this is problematic in terms of having insufficient grounding for the conversation and describe how online designers can compensate for the lack of shared practice by providing a common referent. Finally, the authors discuss three considerations that online designers should take into account in crafting a common referent (the richness of representation provided, the domain specificity required, and how the referent is conceptually framed) and explore their implications for both formal and informal learning environments. (Contains 6 figures.)