In this paper the representation of the knowledge base of firms, research organizations or fields of knowledge as a network will be described. Networks of this type have nodes constituted by units of knowledge defined at a given level of aggregation and links determined by the interactions of such units. Examples of such units are the technological classes associated to patents or the themes that can be identified in scientific publications or patents. The paper will describe the application of this approach to the dynamics of knowledge in firms, research organizations or fields of knowledge by mapping the changes occurring in the structure of knowledge and by measuring some relevant properties of the of the knowledge bases, such as their coherence, variety or cognitive distance. Among other applications this approach can allow us to detect the presence of knowledge discontinuities, such as technological paradigms, and their impact on the behaviour of firms or research organizations.