In recent years, research and development focusing on the synthesis of magnetic nanoparticles have shown wide possibilities for investigation in harnessing their unique properties for numerous potential applications in multifaceted fields. This chapter describes the preparation of zero-, one-, two-, and three-dimensional Fe, Co, Ni, the corresponding core–shell materials. Subsequently, their chemical, electromagnetic, and magnetic properties followed by their magnetic/electrical, catalytic, biomedical, and environmental applications are also described in detail.