The Japanese government and business sector have long seen opportunities in making environmental protection a core feature of industrial policy. The 'green' economic diplomacy-effort, which materialized in the late 1980s and largely builds on targeted domestic innovation policies, is now entering new ground. Assessing recent developments in the railway, nuclear power generation, water, and next-generation automobile industries, this paper analyses how and why the Japanese government uses 'green' environmental and energy technology in relations with emerging and developed countries. Public-private partnerships are strengthened, and semi-governmental institutions and individual politicians take up new roles. Adhering to comprehensive security traditions, Japan's policies aim to contribute to the national interest both in terms of economic prosperity and political stability. Primary objectives are the quest for new markets abroad, resources security, and securing cooperative relations with other countries. Adjustment to shifting global power balances, domestic politics, and climate change challenges also play a role, while 'hard' security issues are barely considered.