Most postsecondary instructors in the United States require students to use textbooks in their courses; however, the cost of commercial materials has increased, and copyright policies impede sharing, editing, and customizations of materials. The current study aimed to examine faculty motivation to adopt Open Educational Resources (OER) and how OER use relates to effective teaching practices. Survey data from 469 professors, instructors, lecturers, and research scientists were analyzed using structural equation modeling, which found that autonomous motivation (engagement with OER textbooks based on enjoyment, value) was the strongest positive predictor of current and future OER textbook use. However, use of OER textbooks was not related to self-reported teaching success. The results of this study contribute to better understanding faculty perceptions of and motivation for OER textbook use, along with informing OER adoption initiatives at postsecondary institutions.