This paper explores knowledge flows, i.e., creation and dissemination of knowledge, in three types of clusters in order to lay a conceptual foundation for analysis of knowledge-based industry clusters. Distinction is made between discovery-driven innovation, represented by Silicon Valley and Cambridge, UK, in semiconductors, and by Boston/Cambridge, the San Francisco Bay Area and Medicon Valley in biotechnology, and design-driven innovation as represented by Boeing in Seattle, Bombardier in Montreal, Airbus in Toulouse, and Saab in Linköping in the aircraft industry. In each cluster, the role of universities and other creators of knowledge is examined. The nature of knowledge dissemination is also analyzed, distinguishing between market-mediated transfers of knowledge and non-market mediated and undirected transfers (“true” spillovers). The role of new start-ups versus incumbent firms in knowledge dissemination and cluster growth is also examined.