Abstract Titanium dioxide (TiO 2 ) is one of the most technologically promising oxides with a broad range of catalytic and photocatalytic activities. Theoretical modeling, especially density functional theory calculations, has been extensively carried out to understand the geometric structure, electronic structure, reactivity, and reaction mechanisms of TiO 2 systems, as well as to develop new catalysts with improved performances. This review summarizes the recent theoretical progress on the well‐defined surfaces of TiO 2 crystalline, and focuses on the structures, adsorptions, and reactions on the surface and at the interface. The theoretical methods and models, surface defects, surface doping, water splitting and H 2 evolution, methanol conversion, CO 2 reduction and CO oxidation, SO x and NO x degradation, CH 4 conversion, organic pollutant degradation, CH bond activation and CC bond formation, dye sensitization, as well as the applications of TiO 2 in some other fields, have been discussed in detail. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis Structure and Mechanism > Computational Matmandatory approximaterials Science Electronic Structure Theory > Density Functional Theory