The IRRI-Japan Collaborative Research Project has been developing new sets of differential varieties for resistance to blast disease (Pyricularia grisea Sacc.) in rice (Oryza sativa L.). The first international standard differential variety set composed of monogenic lines for 24 kinds of resistance genes (Pia, Pib, Pii, Pik, Pik-h, Pik-m, Pik-p, Pik-s, Pish, Pit, Pita, Pita-2, Piz, Piz-5 (= Pi2), Piz-t, Pi1, Pi3, Pi5(t), Pi7, Pi9, Pi11(t), Pi12(t), Pi19(t), and Pi20) was released and has been widely used in various countries. Furthermore, the project has been developing near-isogenic lines (NILs) for blast resistance with three kinds of genetic backgrounds, a Japonica-type variety Lijiangxintuanheigu (LTH), an Indica-type variety CO39, and a newly developed ‘universal susceptible’ line US-2 which was derived from a cross between Indica and Japonica-type susceptible varieties. A total of 23 lines for 14 kinds of resistance genes, Pia, Pib, Pik, Pik-h, Pik-s, Pita, Pita-2, Piz-5 (= Pi2), Piz-t, Pi1, Pi3, Pi5(t), Pi7, and Pi9, have been developed by the recurrent backcross method using the monogenic lines with the LTH genetic background. Twenty lines for 14 kinds of resistance genes, Pib, Pik, Pik-h, Pik-m, Pik-p, Pik-s, Pish, Pita, Pita-2, Piz-5 (= Pi2), Piz-t, Pi1, Pi5(t), and Pi7 have been developed with the CO39 genetic background. Moreover, a universal susceptible rice line, US-2, which has not been known to have any blast resistance genes in the genetic background, and can be cultivated easily under both tropical and temperate conditions, is also being used for the development of NILs as the next generation of differential varieties. These lines are offered as gene sources for breeding of blast resistance and as sets of international standard differential varieties used for the study of blast disease.