Research, education, and extension investments, while usually necessary, are often insuffi cient alone to bring knowledge, technologies, and services that enable farmers and entrepreneurs to innovate. Efforts to strengthen research systems and increase the availability of knowledge have not increased innovation or the use of knowledge in agriculture at the pace or the scale required by the intensifying and proliferating challenges confronting agriculture. Agricultural Innovation Systems: An Investment Sourcebook contributes to the identifi cation, design, and implementation of the investments, approaches, and complementary interventions most likely to strengthen agricultural innovation systems (AIS) and to promote innovation and equitable growth. The Sourcebook provides a menu of tools and operational guidance, as well as good practice lessons, to illustrate approaches to designing, investing in, and improving these systems.