This paper reports preliminary results from a study that examines factors influencing knowledge sharing among members of business clusters based in Wellington, New Zealand. Business clusters are local concentrations of competitive firms in related industries that do business with each other. Earthquake Engineering, Creative Capital, Natural Hazards, Optics and Software are examples of clusters stu-died in this paper. However, some of the companies in many business clusters are direct competitors in the local arena and they are often expected to co-operate and share business knowledge with each other when they are considering bidding for international projects or contracts. This knowledge may be considered to have provided each company with a competitive advantage. Therefore, trying to successfully operate in this mixed environment of "co-operation" and "competition" can pose a dilemma for many members of business clusters. For this study, a three-stage data collection strategy was used: a focus group, online voting exercise and individual interviews. Representatives from seven business clusters in the Wellington region took part in this study. Analysis of the data revealed that several factors do influence knowledge sharing in business clusters, such as: sharing a common understanding and commitment to the cluster idea; initial respect and trust between cluster members; and having strong, charismatic cluster champions/leaders. These factors will be explored and the implications for practice and research will also be discussed.