Understanding Physics is a completely revised, updated, and expanded e- tion of the Project Physics Course. It is an integrated introductory physics course, developed with funding from the Carnegie Corporation and the Sloan Foundation and with the close cooperation of Springer-Verlag New York. In approach and content, Understanding Physics follows the trail blazed by the earlier versions, but it includes more recent developments in physics and a stronger emphasis on the relationships among physics, technology, and society. We have sought especially to incorporate the salient lessons of recent physics education research and practical experience gained in the classroom. The Audience Understanding Physics is written primarily for undergraduate college s- dents not intending (at least initially) to enter careers in science or en- neering. These may include liberal-arts students, business majors, prelegal, and prospective architecture students. We have found that when the course is taken with laboratory work, it has been deemed suitable by medical schools for premedical students.