Magnetic nanoparticles (MNPs) have many applications in the biomedical field because of their non-toxicity, high chemical stability, and biocompatibility. They are used in DNA or protein separation, hyperthermia, tissue engineering, magnetic resonance imaging, cancer therapy, drug delivery, bone and dental repair, biosensors, etc. The book focuses on magnetic nanoparticles and coated nanoparticles (ferrites nanoparticles, bimetallic-magnetic nanoparticles, magnetic fluid); their synthesis, characterization, and in vivo or in vitro biomedical applications. Keywords: Iron Oxide Magnetic Nanomaterials, Magnetic Spinel Ferrite Nanoparticles, Magnetic Oxide Nanoparticles, Ferromagnetic Nickel Nanostructures, Cobalt Ferrite with Niobium Pentoxide, Hyperthermia, Oncologic Magnetic Thermotherapy, Cancer Therapy, Cancer Diagnosis, Drug Delivery. Immune System Related Diseases.