Japan has been described as ‘the land of cooperatives’. This chapter looks at the long history of agricultural, consumer and medical cooperatives in Japan, and explores the role of cooperatives in Japan’s informal life politics by focusing particularly on the story of one experiment in cooperative medicine: Saku Central Hospital in Nagano Prefecture, founded in 1944. In the first half of the twentieth century, cooperatism in Japan was promoted both by the government, which saw it as a means of combatting political radicalism, and by some left-of-centre activists who saw it as a path to fundamental social reform. During the 1930s, the Christian social reformer Kagawa Toyohiko gained international fame for a social vision (particularly influential in the United States) centred on cooperatives. Building on aspects of these diverse traditions, Saku Central Hospital was the starting point for an innovative postwar program of rural medicine, in whose development the hospital’s second director, Wakatsuki Toshikazu, played a key role. The hospital’s philosophy defined ‘health’ as a social phenomenon whose scope went far beyond the immediate treatment of diseases. This social vision of health care has had widespread influence in Japan and other parts of Asia.