Nanoferrites represent a transformative class of magnetic oxide materials exhibiting exceptional electromagnetic properties that arise from the synergistic coupling of magnetic and dielectric responses at the nanoscale. This chapter provides a comprehensive examination of the fundamental electromagnetic behavior of nanoferrites, exploring the intricate interplay between compositional variations, structural parameters, and processing conditions that govern their performance in advanced technological applications. The discussion encompasses the theoretical framework based on Maxwell's equations and complex electromagnetic parameters, including frequency-dependent permeability and permittivity, magnetic and dielectric loss mechanisms, and resonance phenomena described by the Landau-Lifshitz-Gilbert equation. Particular emphasis is placed on nanoscale effects, including enhanced surface-to-volume ratios, altered magnetic domain configurations, quantum confinement phenomena, and the critical transition from multi-domain to single-domain behavior at particle sizes below 50 nm. The chapter systematically analyzes dielectric properties arising from electronic, ionic, dipolar, and interfacial polarization mechanisms, as well as magnetic properties influenced by exchange interactions, magnetic anisotropy, and spin dynamics. Advanced topics including magneto-dielectric coupling, microwave absorption characteristics, electromagnetic interference shielding mechanisms, and ferromagnetic resonance are thoroughly examined. The influence of synthesis methodologies—including sol–gel, co-precipitation, and hydrothermal techniques—on electromagnetic performance is critically evaluated, along with the strategic role of rare-earth and transition metal doping in tuning electromagnetic responses. Theoretical modeling approaches and advanced characterization techniques, including vector network analysis, impedance spectroscopy, and ferromagnetic resonance spectroscopy, are discussed as essential tools for understanding structure–property relationships. Emerging applications in high-frequency electronics, electromagnetic wave absorption, magnetic recording media, biomedical devices, and next-generation wireless communication systems are explored, highlighting the technological significance of nanoferrites. The chapter concludes by addressing current challenges related to synthesis reproducibility, property optimization, computational modeling accuracy, and scalability, while outlining future research directions toward the rational design of multifunctional nanoferrite-based electromagnetic materials and devices for sustainable and efficient electromagnetic technologies.