The term Satoyama, although used in some local contexts since the Edo-period, did not appear in dictionaries of Standard Japanese until 1989. Introduced by Prof. Shidei Tsunahide, a forester ecologist at Kyōto University, in his publications of the 1960s and 1970s, it has evolved and spread widely during the last 15 years, becoming a keyword of our time, not only in Japan. This is an extremely interesting case of word formation and semantic change in view of ecology and its theoretical, practical and political implications. Satoyama was at first applied to a border zone of forests and secondary woodlands adjunct to small villages and farming areas. It has quickly evolved, though, to include grasslands, rice paddies, wetlands, irrigation ponds and the whole surroundings of rural dwellings. Today it refers to a traditional Japanese landscape in the countryside, a zone of particularly rich biological diversity in which humans and nature coexist ideally in a symbiotic relationship. This article documents the development of this new concept by analyzing dictionary entries and other texts, and introducing important sources, books, and magazines, mostly in Japanese.