In this book, cancer theranostics applications of magnetic iron oxide nanoparticles are overviewed in detail. Moreover, their synthesis, characterization, multifunctionality, disease targeting, biodistribution, pharmacokinetics and toxicity have been briefly highlighted. Finally, we have mentioned the current examples of clinical trials of magnetic nanoparticles in cancer theranostics, along with their future scopes and challenges. Part of IOP Series in Photomedicine and Biophotonics