Social network analysis (SNA) is a methodological approach to measuring and mapping relationships. It can be used to study whole networks, all of the ties within a defined group, or connections that individuals have in their personal communities. The resulting graph-based structures illustrate the composition and effectiveness of networks on a variety of levels. Programs that can benefit from a social network perspective are common in evaluation research. As part of a process evaluation, SNA can shed light into the "black box" of how and why people and groups interact. This brief introduces the concepts behind SNA and illustrates how to use this method in process and outcome evaluations. (Contains 4 figures, 1 table, and 1 footnote.)