Asianism has often been discussed in Anglophone literature as rhetoric used to justify Japan’s imperial expansion. Yet both the genesis of the concept prior to World War II and its evolution in the post-World War II era have received less attention. This chapter examines how shifting conceptions of Asianism have influenced Japan’s foreign policy stance and international cooperation development agenda. By tracing the historical roots, development and diffusion of Asianism from its origins in early Meiji Japan to present, the chapter shows how Asianism, though its influence has declined over time, has endured in the post-war era through the concept of Asian regionalism.