This is a reprint of a Special Issue of Energies, titled "Condition Monitoring and Failure Prevention of Electric Machines". This Special Issue primarily focused on the issues related to the advanced monitoring, diagnosis, and prevention of typical and complex faults in all kinds of electric machines. Four guest editors, namely Prof. Yu-Ling He (Department of Mechanical Engineering, North China Electric Power University, China), Prof. David Gerada (PEMC group, University of Nottingham, UK), Prof. Conggan Ma (School of Automotive Engineering, Harbin Institute of Technology, China), and Prof. Haisen Zhao (School of Electrical and Electronics Engineering, North China Electric Power University, China), worked together on this Special Issue.