What is the structure of the Earth? What better place to begin our exploration of the Solar System then with the best-studied planet, the Earth. This lecture discusses the interior structure of the Earth, introducing the idea of differentiation, how geologists map the interior of the Earth using seismic waves, and the origin of the Earth's magnetic field. We then discuss the crust of the Earth, which is divided into 16 tectonic plates, and explore how plate motions driven by convection in the upper mantle have shaped the visible surface of our planet over its dynamic history. Recorded 2006 Oct 31 in 100 Stillman Hall on the Columbus campus of The Ohio State University.