Pretty vacant. Oxide surfaces are continuously finding new applications in advanced technologies such as corrosion protection, thermal coating, catalysis, sensors, microelectronics, magnetic properties, etc. A understanding of the microscopic properties of oxide surfaces is closely related to the identification of the surface defects. Oxygen vacancies (see bright spots in picture) are particularly important defects but also very difficult to characterize. Recent advances in the use of STM allows one to follow the dynamics of the migration of oxygen vacancies on an oxide surface. Starting from a recent example of application of dynamic STM to TiO2, the role of oxygen vacancies on the chemistry of oxide surfaces is highlighted.