This publication provides an introduction to the theory of plate tectonics. It was intended as a companion to the map entitled 'This Dynamic Planet', published by the U.S. Geological Survey (USGS) and the Smithsonian Institution. Topics include the history and development of the theory, lines of evidence, plate motions and interactions, hotspots, what drives plate motion, and extraterrestrial plate tectonics. It can be viewed online, downloaded, or purchased in hardcopy. Ordering information is provided. Educational levels: Middle school, High school, Undergraduate lower division