We present a combined experimental and theoretical study of surface-related magnetic states in TiO2. Our experiments performed on nano-sized thin films of pure TiO2 have suggested that the observed room-temperature magnetism originates from defects, particularly from the surface of thin films as well as from point defects, such as vacancies located mainly at the surface. To clarify this phenomenon, we performed quantum-mechanical density functional theory (DFT) calculations. Our fixed-spin-moment calculations identified both the bulk and the bulk-like TiO2-terminated vacancy-free (001) surfaces as non-magnetic. In contrast, oxygen vacancies in the TiO-terminated and TiO0.75-terminated (001) surfaces led to ferromagnetic and rather complex ferrimagnetic states, respectively. The spin-polarized atoms are the Ti atoms (due to the d-states) located in the surface and sub-surface atomic planes. Finally, the O-terminated surfaces are also magnetic due to the surface and sub-surface oxygen atoms and sub-surface Ti atoms (however, their surface energy is high). For further details, see Friák et al., Journal of Applied Physics 134, 013902 (2023), DOI: 10.1063/5.0155282.