In this article, we argue that although mathematics educators are concerned about social issues, minimal attention has been paid to student-student interactions outside the classroom. We discuss social network analysis as a methodology for studying such interactions in the context of an undergraduate course. We present results on the questions: Who studies with whom? What are students' study habits, and are these systematically related to the habits of those with whom they interact? Do individual and collaborative study habits predict attainment? We discuss the implications of these findings for research on undergraduate learning and on social issues in mathematics education, suggesting that social network analysis may provide a bridge between mathematics education researchers who focus on cognitive and on social issues.