Researchers have examined many strategies for instructor preparation, but the role of common textbooks has received little attention, despite Yancey listing them as an essential feature to consider in developing instructor preparation. This case study examines the impact of the custom common textbook on graduate and professional instructors in a First Year Writing program at a large Midwestern research university. Data were collected through a survey, focus groups, and interviews with instructors, as well as interviews with textbook authors. I found that although instructors varied widely in their use of the text, it did contribute to instructor preparation by influencing choices of content and awareness of program culture and values, especially for experienced instructors. Although additional instructional preparation measures are necessary for new instructors, common textbooks should not be ignored in research and assessment of instructor preparation strategies.