TEXTBOOK CONTENT is one of the most significant influences on faculty’s course planning decisions, but with the growth of the World Wide Web in recent years, the nature of the textbook has changed considerably. Many publishers now offer Web-based supplements to social science textbooks, but no tools exist for instructors to evaluate the resources that these supplements offer. Building on the work of Wilkinson, Bennett, and Oliver (1997), I develop evaluation criteria for these supplements in order to measure how a textbook Web site can enhance teaching and learning. The metric includes measures of site access and usability, resource identification and documentation, information structure and design, navigation within the document, quality of links, aesthetic and affective aspects, and pedagogical/disciplinary needs. Examples of applications of the criteria to popular sociology texts are provided.