This document introduces open educational resources (OER) and open textbooks. It discusses how rising textbook costs, student advocacy, and new licensing models have enabled the development of OER. Open textbooks offer benefits like customization, immediate updates, and low or no cost to students. While concerns remain around quality and transition efforts, open textbooks present an affordable alternative to commercial materials. The document provides examples of open textbook models and resources for discovering, selecting, adopting, and using open textbooks in courses.