In this work we review our theoretical investigation of TM-doped rutile TiO₂ system (TM: Mn, Fe, Co, Ni, and Cu) for different concentrations and distributions of these impurities. The effect of oxygen vacancies on the magnetic moments and the magnetic alignment for pure and doped TiO₂ is studied as a function of vacancy concentration and distribution. We also review the experimental work done in our laboratory using X-ray absorption, magnetometric techniques and Mössbauer spectroscopy. The combined theoretical and experimental studies enabled us to characterize the local structure around the TM impurities in rutile TiO₂ unambiguously and support the conclusion that oxygen vacancies are fundamental for the ferromagnetic response of these systems, explaining the diversity of magnetic moments observed experimentally for samples grown in different conditions.