In both developed Western nations and developing countries, economic growth was based on the development of industrial districts, which were much more organized and institutionalized in modern Japan than economist Alfred Marshall had described. Local trade associations played an important role in enhancing Marshallian externalities, arising from the ease of imitating improved ideas and transacting unfinished products among clustered enterprises by facilitating joint actions in the supply of public goods, such as through the creation of local district brands and through the efficient provision of business information. These activities were clearly beyond the scope of agglomeration economies. This article examines the case of Kiryu, one of the best-known silk weaving districts in Japan.