A rising competitive pressure for innovations comes along with an increasing number of companies and public research facilities that include external sources of information into the innovation process. This trend towards an open innovation process can be verified empirically. External R&D expenditures are those invested in R&D activities outside the firm's boundaries, e. g. license fees, research assignments or collaborations with public research institutes and companies. Investments in external R&D allow fast adaptations within the innovation process in case of changing market trends or radical innovations. Furthermore, opening up the innovation process simplifies an integration of required know-how from another industry. Altogether, the flexibility of innovation can be increased without an expansion of a company's own capacities. Beside the trend of integrating knowledge from outside the firm's boundaries, an increasing internationalization of R&D can be observed in several branches. Hence, this article examines the following questions: Which factors determine the absorptive capacity of national economies? How can these factors be operationalized and how can an adequate framework be developed to increase national absorptive capacity?