Objectives. This article explores the impact of email on the network structure of small, voluntary associations. By focusing on the density and centralization of associations, we illuminate how the Internet affects their cohesiveness and democratic character. Methods. Based on network data collected from 41 community-based associations that are comparable on a variety of factors known to influence network structure, we employ multiple regression techniques to explore the impact of increased email use on group- and individual-level network measures. Results. We find that the technological nature of email as well as the background, interests, and intentions of its users interact to influence density and centralization. Individuals employ electronic mail differently from other communication modes such as phone and face-to-face communication. Network density increases, and network centralization either increases or decreases, depending on the distribution of email use in the association. Conclusions. These effects on associational structure are likely to have significant long-run impacts on the cohesion, efficacy, and democratic character of voluntary associations.