Purpose – This main aim of this article is to explore the relationship between knowledge management (KM) and communities of practice (CoPs) in general and virtual CoPs in particular. A subsidiary aim is to provide some practical guidelines about how virtual CoPs can be facilitated and maintained. Design/methodology/approach – The relationship between KM and CoPs is explored using theoretical constructs, the notion of a duality, and data from a case study. The article reports on a case study of a ‘‘virtual’’ CoP and highlights two key aspects of virtual working. The article demonstrates how these key aspects map on to Wenger’s participation-reification duality and, in turn, on to the soft-hard duality described by Hildreth and Kimble. Findings – The case study of a ‘‘virtual’’ CoP was based in three geographically separate locations (the UK, the USA, and Japan). The case study reports on the activities of the UK part of the CoP both at their UK base and during one of their regular trips to the USA. It highlights the importance of two particular aspects or virtual working: social relationships and the use of shared artefacts. Practical implications – Some general conclusions are drawn from the analysis concerning the facilitation of virtual CoPs and the broader implications of dualities for KM. Originality/value – The main contribution of the article is in making an explicit link between KM and CoPs through the use of the notion of the duality of knowledge.