Defect sites in titania have a substantial effect on many thermal and photochemical reactions. Three common types of defects are titanium interstitials, oxygen vacancies and oxygen adatoms—all of which can react with organic molecules adsorbed on the surface. We look broadly at thermal reduction and photochemical oxidation reactions of oxygenates. In particular, we focus on the reductive coupling of benzaldehyde, the photo-oxidation of butyrophenone, the photostability of benzoic acid, and the photo-oxidative coupling of methanol to methyl formate. Methods used include temperature programmed reaction spectroscopy, scanning tunneling microscopy, and density functional theory.