This chapter analyzes rare earth (RE)-doped metal oxides in piezoelectric and triboelectric energy devices. RE elements, with unique 4f electron configurations, significantly affect the structural and functional properties of oxides. Their incorporation in systems like MOFs, perovskites, and nanoparticles enhances interfacial interactions, charge mobility, and polarization for efficient energy harvesting. The chapter examines how RE doping improves electromechanical coupling and raises output voltages by modulating the dielectric and ferroelectric characteristics that are crucial for piezoelectric devices. Through processes like band structure tuning, the formation of oxygen vacancies, and surface energy modification, RE-doped oxides improve surface charge density and charge transfer efficiency in triboelectric nanogenerators (TENGs). Improved carrier dynamics, surface potential, and dielectric constant—parameters that directly affect piezoelectric and triboelectric performance—are demonstrated in case studies of materials such as Ce-doped ZnO, Gd-doped CeO2, and Eu-doped La2O3. Multipurpose systems like Cu-doped WO3 and Sm-doped Sc2Mo3O12 show that RE doping enhances energy conversion and adds functionalities such as magnetocaloric effects and negative thermal expansion. This chapter provides valuable insights into the synthesis and design of RE-doped oxides for advanced energy devices. It is especially useful for researchers developing self-powered, sustainable electronics, and sensors.