The International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) is one of 15 CGIAR centers and takes part in agricultural research and development in the most marginal regions of the world. Over the past 40 years, many Japanese scientists/projects have worked towards the improvement of crop production and betterment of livelihoods in the semi-arid tropics in both in Asia and Africa, some of which were supported by the Japanese Government and/or implemented by Japan International Research Center for Agricultural Sciences. In this paper, we review the significant scientific contributions of Japanese scientists to ICRISAT’s goals for each grand research theme.