In recent years, iron oxide magnetic nanoparticles have played an important role in the development of next generation nanomedicine for disease diagnosis and treatment. This book discusses many important aspects of this type of nanomaterial, including several popular preparation methods for iron oxide nanoparticles, the principle and common process for their subsequent functionalization and their potentials in clinical applications. It will introduce several novel low cost, large scale synthesis methods that can quickly produce iron oxide nanoparticles that are suitable for nanomedicine fabrication. It also presents a few interesting demonstrations of iron oxide nanoparticles being applied in controlled target drug delivery and bioseparation area.