Because of the size and shapes of the d-orbitals, electron-electron repulsions play an important role in determining their conductivity of transition metal compounds. After introducing the Hubbard model, a common approach to modeling this behavior, we take a closer look at the conductivity of transition metal oxides with the rock salt and perovskite structures. This lecture was designed and delivered by Patrick Woodward for use in the course Solid State Chemistry (Chem 7330) at Ohio State University.