Defects strongly affect the physical and chemical properties of metal oxide surfaces, and step edges are the most common type of defects. On nanoparticles the high concentration of step edge atoms may even dominate surface chemistry. Atomic-scale descriptions of metal oxide step edges are scarce. We report first-principles calculations of the structure, energetics, and chemistry of step edges on the (101) surface of TiO2 anatase, an important photocatalytic material. A procedure based on systematic calculations of related vicinal anatase TiO2 surfaces has been used, which yields step edge energies with remarkable accuracy. The electronic structures of the stepped surfaces and adsorption of prototype molecules have been also investigated. The present results allow us to obtain a detailed and complete understanding of available experimental observations. In particular, predictions of step edge configurations are in excellent agreement with Scanning Tunneling Microscopy measurements. @FootnoteText@ *Work in collaboration with Xue-Qing Gong, Department of Chemistry, Princeton University; Matthias Batzill and Ulrike Diebold, Department of Physics, Tulane University.