Drawing on data from interviews with mathematics faculty in three different types of undergraduate institutions and using Rabardel's model of instrument use (Verillon & Rabardel "1995"), we describe three ways textbooks mediate college faculty work regarding instruction. The model anticipates epistemic and pragmatic mediations between the instructor and teaching, others, and self, with the textbook playing a significant role. We provide illustrations of each of these mediations as described by the participants. Pragmatic rather than epistemic mediations were more common. In addition, we found that the mediations seem largely dependent on instructors' categorical perceptions of their students, either as "math students" or as "undergraduate students". These alternate perceptions resulted in different descriptions of schemas for using the textbook with each type of student. The analysis generates further questions for research regarding either a developmental component or a curricular component that could explain this categorization of students. (Contains 2 footnotes, 2 tables, and 2 figures.)