The established theory argues that pre-war Japan's perspective of Southeast Asia was mainly concerned with its natural resources. However, this book on ethnologist Matsumoto Nobuhiro shows that scientific study of Southeast Asian culture had already existed in this time. It traces the formation and development of Matsumoto's ideas on Southeast Asia based on his writings in the period 1919-1945. Matsumoto started studying this region from evolutionist ethnology and decided to focus on it under the influence of diffusionist ethnology, because he believed in significance of Japan's relation with Southeast Asia in ancient times. In the 1930s and 1940s, he established Southeast Asian studies and Vietnamese studies by bringing research materials from French Indochina to Japan, introducing them to the Japanese people and founding research institutes at Keio University. He acquired various theories from Western and Japanese scholars and somewhat adjusted his arguments to the political climate of the era. This book examines evolutionist, sociologist and diffusionist ethnology, Southern Culture Theory, Southward Theory, Climate Theory, Orientalism, Southern Advance Theory, and Pan-Asianism in his works. It reveals that Matsumoto's perspective of Southeast Asian culture was a patchwork of arguments from many theories. In this pattern, he offered multiple views on this culture, which instigated further development of Southeast Asian studies in diverse fields, but his conclusion on Japan-Southeast Asian relations remained ambiguous.