Iron oxide-based magnetic nanoparticles (IONP) that display high saturation and high magnetic susceptibility are of great interest for biotechnological and biomedical applications. Magnetite displays strong ferrimagnetic behaviour and is less sensitive to oxidation than other magnetic transition metaloxides. It is then not surprising that IONP include magnetite in their formulation. The role of IONP technology in the cited areas requires specific characteristics with regard to the particle size and surface functionality. Therefore the incorporation of polymeric moieties appears as a valuable tool to achieve the desired properties. On this context surface-modified IONP and magnetic nanocomposites (MNC) can be obtained depending on the role of the polymeric network in the formulation process. The methods to prepare  each kind of magnetic-polymeric composite are reviewed in this work. First, the different kinds of IONP are carefully analyzed and second, the techniques available to incorporate polymer and other modifiers, are addressed. An investigation of the relationship between the nature of the modifier and the tailored application of the generated particles is also included with the focus mainly in the effect of some experimental variables on the nanoparticle size. Finally, two specific applications of magnetic nanocomposites in novel and relevant fields will be discussed. The role of magnetic nanoparticles as drug delivery systems (DDS) is of high significance and consequently, the available information is rich, but it is mostly dedicated to the sustained release of anticancer drugs. Here we will show other drugs, able to be delivered from magnetic DDS. MNC have recently emerged as effective supports for lipase immobilization. The reported data concerning to this topic is still quite limited and therefore novel published advances are reviewed here. Buy this Article