The interest in the analysis of library user behavior has been increasing rapidly since the advent of digital libraries and the Internet. In this context, the authors analyze the queries posed to a digital library and recorded into the Z39.50 session log files, and construct communities of users with common interests, using data-mining techniques. One of the main concerns of this study is the construction of meaningful communities that can be used for improving information access. Analysis of the results brings to the surface some of the important properties of the task, suggesting the feasibility of a common methodology.