Social capital constitutes the cultural component of modern societies. Building social capital has typically been seen as a task for ‘second generation’ economic reform, but unlike economic policies and institutions, social capital is not created or shaped by public policy but is inherited throughout local communities successive generations. Enhancing social capital therefore is about promoting local knowledge deeply rooted into local communities’ practices on land and at sea. In Japan, the culturally specific interaction of humans with nature has led to the emergence of specific socio-ecosystems called ‘satoyama’ on the land side and ‘satoumi’ on the coast and sea side. Here, characteristics of related local knowledge include information about consumed products like wild edible plants or seaweeds, and learning by doing practices like traditional rice cultivation or sea ranching. This knowledge has been developed over centuries and has been handed down from generation to generation. There are actually other types of satoyama and satoumi which have been flourishing around the world though the latter (satoumi) probably has no equivalent in other countries’ coastal areas because of the unique Japanese fishing rights system. First largely ignored as a social capital, satoumi has emerged as a new concept only a few years ago. In the frame of the recently adopted national ocean policy such a social capital, like it may be found in other countries, should not be ignored when addressing integrated coastal zone management processes and tools for the sake of sustainable coastal development in Japan and elsewhere in the world.