Dense social networks are thought to be a pre-requisite for innovation-led economic growth and, as a result, building socalled "knowledge networks" has become an important goal for some policy-makers. This has certainly been the case among "rust belt" communities where innovation and economic growth historically depended on the activities of very large industrial companies. The restructuring of those companies in the 1980s focused the attention of policy makers and regional economic leaders on ways to rebuild regional innovative capacity and much of this attention has been directed toward building up knowledge networks. Drawing on structured interviews as well as data from a unique longitudinal and network analysis of inter-organizational relationships, this paper presents empirically grounded case studies of two well-matched mature industrial cities that were simultaneously subjected to these forces: Akron, Ohio and Rochester, New York. Until the 1980s, Akron, Ohio was known as the "tire capital of the world." But by 1997, not a single car tire was produced there. Nevertheless, many of the tire companies--or at least parts of them--maintained R&D facilities in the region while shifting their emphasis toward advanced polymer technologies (the general class of materials which include synthetic rubber, fibers and engineered plastics). Similarly, Rochester, New York was home to several internationally prominent optics and optical-electronic companies. In the 1980s, these companies moved significant parts of their production process out of the region, and the community has pursued efforts to develop a base of high-tech photonics and opto-electronics firms since. Despite the similarity of their situations, the policies and practices employed to rebuild knowledge networks differed. In Akron, those efforts were directed toward generating a strong identity among local actors while offering a "window" into technology coming out of the prominent university's labs as a kind of inducement to participation--an approach which I refer to as a "fountain" approach. In Rochester, on the other hand, efforts were directed more toward forging relationships among local actors through a variety of opportunities for collaboration--a "forum" approach. The results indicate that the forum approach has been more effective both in terms of re-building the region's intellectual network as well as in terms of spurring the creation of innovative companies. More generally, the results point to a number of implications for how policy can more effectively help to build "social capital" within communities undergoing acute economic crises.