In many industries, production resides in a small number of highly concentrated regions; for example, several high tech industries cluster in Silicon Valley. Explanations for this phenomenon have focused on how the co-location of ﬁrms in an industry might increase the efﬁciency of production. In contrast, this article argues that industries cluster because entrepreneurs ﬁnd it difﬁcult to access the information and resources they require when they reside far from the sources of these valuable inputs. Since existing ﬁrms often represent the largest pools of these important factors, the current geographic distribution of production places important constraints on entrepreneurial activity. As a result, new foundings tend to arise in the same areas as existing ones, and hence reproduce the industrial geography. In support of this thesis, the article reviews empirical evidence from the shoe manufacturing and biotechnology industries.