Nanoferrites, a class of spinel-structured magnetic oxides, have emerged as multifunctional materials with wide-ranging applications in electronics, biomedicine, and energy technologies. Their unique properties, including tunable magnetism, high electrical resistivity, and biocompatibility, are strongly influenced by temperature and frequency, making the study of these dependencies critical for technological deployment. This chapter provides a comprehensive overview of the structural, magnetic, and dielectric responses of nanoferrites under varying thermal and electromagnetic conditions. The discussion emphasizes temperature effects on saturation magnetization, coercivity, Curie temperature, and spin relaxation mechanisms, while also addressing frequency-dependent behaviors such as dielectric dispersion, AC conductivity, magnetic permeability, and eddy current suppression. Particular attention is given to the role of cation distribution, doping strategies, and surface effects in modulating these responses. Experimental insights from magnetometry and impedance spectroscopy are integrated with case studies to link fundamental mechanisms to applications in EMI shielding, magnetic hyperthermia, sensors, and microwave absorbers. Finally, challenges in achieving stability under extreme conditions are highlighted alongside future strategies, including doping, core–shell architectures, and composite design. The chapter establishes a holistic structure–property–function relationship framework, underscoring the central role of nanoferrites in next-generation multifunctional devices.