Successful firm-level innovation depends on the development and integration of new knowledge into the innovation processes, which usually comes from different sources. Largely, industrial and innovation economics literature studies the degree to which internal and external knowledge sources are complementary or substitutes for the innovation process. This chapter discusses the relevance of innovation complementarities for developing economies with a specific focus on policy implications. As an illustrative case, the chapter presents an application of modern complementarity tests (super and sub modularity tests) to a knowledge-intensive business services sector from an emerging economy. The chapter uses technological micro data of software firms in Argentina and considers estimation results in light of industrial policy implemented in the country.