This chapter analyses and extends existing studies of how to characterise, trace and measure knowledge bases of firms, sectors and countries. The chapter is structured in two main parts. First, we present the concepts of knowledge specialisation and knowledge integration as the relevant dimensions along which knowledge bases can be mapped. The concepts proposed build upon extensive qualitative research that has focused on a variety of processes of knowledge generation and use in a range of industrial sectors and organisations. The aim of this chapter is to demonstrate that these, largely qualitative, processes map into key characteristics of the knowledge bases they contributed to generating and shaping; and that these key characteristics can be measured relying on the innovative use of patents, citations and publications data. More specifically, the analysis of the evolution of knowledge specialisation over time provides information about the persistence of knowledge in firms and sectors. It hints at the cumulative, path dependent nature of learning processes. Integration is studied by analysing the evolution of specialisation across different typologies of research. It hints at the complex, non-linear interdependencies that link the scientific and technological domains. The second part of the chapter will be devoted to the presentation of indicators of breadth and depth that capture the key characteristics of the concepts introduced in the first part.