Magnetic nanoparticle theranostics will be discussed as a novel method to target brain tumors with MRI guidance. Both antibody conjugated magnetic iron-oxide nanoparticles (IONPs) and free IONPs will be discussed. MRI-guided convection-enhanced delivery (CED) will be introduced as an optimal delivery method for magnetic nanoparticle theranostic targeting of brain tumors in multiple rodent glioma models. Preliminary feasibility and efficacy results of an antibody conjugated magnetic nanoparticle theranostic utilized in a canine spontaneous glioma trial will be shown. Future work involving a magnetic nanoparticle theranostic with trimodal functionality (targeted cell therapy, hyperthermia, and MR imaging) will be introduced.