An innovation system can be defined as a network of organizations, enterprises and individuals focused on bringing new products, new processes and new forms of organization into use, together with the institutions and policies that affect their behaviour and performance. In this chapter, we present an agricultural innovation systems (AIS) approach to understanding the role of research in agricultural innovation, with a focus on the case of research into sustainable maize intensification. We consider three important stages of an innovation process: the identification of problems and targeting of interventions, local experimentation and bringing new ideas into routine use. We discuss the role of research at each stage, and then argue that an AIS approach mandates increased focus on the personal, organizational and institutional capacities of researchers and research bodies.