This article provides an introduction to geographic information systems (GIS) and how the technology can be used to enhance evaluation practice. As a tool, GIS enables evaluators to incorporate contextual features (such as accessibility of program sites or community health needs) into evaluation designs and highlights the interactions between programs and their environments. Evaluators can formatively utilize GIS to examine implementation issues and their connections to the communities served and summatively to study program impacts and the factors contributing to variations between program sites. Improvements in technology as well as in data storage and access make this a feasible tool for a broader range of users. Through a hypothetical case study, the article discusses the strengths, limitations, and future trends of GIS in the context of the evaluation field. (Contains 4 figures.)