This chapter describes the fundamental properties of magnetic nanomaterialsMagnetic nanomaterials, emphasizing their unique behaviours and the principles that govern them at the nanoscale. The main magnetic propertiesMagnetic properties such as superparamagnetism, coercivityCoercivity, and magnetic anisotropyMagnetic anisotropy are explored in detail, highlighting how these characteristics differ from their bulk counterparts. The influence of particle size, shape, and composition on magnetic behaviour is systematically analysed, revealing the critical role these parameters play in tuning the properties of nanoparticlesNanoparticles. Real-world applicationsApplications, ranging from catalytic applicationsCatalytic applications and environmental remediationEnvironmental remediation to data storageData storage and energy technologies, are discussed to underscore the practical significance of these materials. By bridging theoretical insights with practical implications, this chapter provides a comprehensive understanding of the magnetic phenomena that underpin the design and functionality of magnetic nanomaterialsMagnetic nanomaterials in diverse technological domains.