This chapter contains sections titled: Introduction Ta Substitution in TiO2: Doping or Alloying? Diluted Magnetic Semiconductors (DMS) Defect-Mediated Ferromagnetism Magnetic Impurity Analysis in Ti1-xTaxO2 System Defect-Induced Ferromagnetism in Ti1-xTaxO2 Film First-Principles Spin-Polarized GGA + U Calculations Mechanism of Defect-Mediated FM Optimization of Ferromagnetism Outlook for Defect-Mediated Properties of Ti1-xTaxO2 References © 2013 Wiley-VCH Verlag GmbH & Co. KGaA.