Electron dynamics at molecular−bulk interfaces play a central role in a number of different fields, including molecular electronics and sensitized semiconductor solar cells. Describing electron behavior in these systems is difficult because it requires a union between disparate interface components, molecules and solid-state materials, that are studied by two different communities, chemists and physicists, respectively. This Account describes recent theoretical efforts to bridge that gap by analyzing systems that serve as good general models of the interfacial electron dynamics. The particular systems that we examine, dyes attached to TiO 2 , are especially important since they represent the key component of dye-sensitized semiconductor solar cells, or Grätzel cells. Grätzel cells offer a cheap, efficient alternative to traditional Si-based solar cells. The chromophore−TiO 2 interface is a remarkably good target for theorists because it has already been the subject of many excellent experimental investigations.