The cover picture of Earth was taken by the crew of the Apollo 17 on their journey to the moon on December 7, 1972 (from I’m grateful to Laurie Houston, Susanne Capalbo, Kathleen Dean Moore, and Michael Paul Nelson for their contributions to the chapters on economics and ethics. I want to thank my wife Susanne for her support and patience on many evenings and weekends that I spent writing. I appreciate student’s comments, which have improved the book. I also want to thank Dianna Fisher, Gabe Higginbotham, and Devin Curtis from OSU’s open textbook project for their encouragement and technical help.