Magnetic　iron　oxide　nanoclusters,　which　refers　to　a　group　of　individual　nanoparticles,　have　recently　attracted　much　attention　because　of　their　distinctive　behaviors　compared　to　individual　nanoparticles.　In　this　review,　we　discuss　preparation　methods　for　creating　iron　oxide　nanoclusters,　focusing　on　synthetic　procedures,　formation　mechanisms,　and　the　quality　of　the　products.　Then,　we　discuss　the　emerging　applications　for　iron　oxide　nanoclusters　in　various　fields,　covering　traditional　and　novel　applications　in　magnetic　separation,　bioimaging,　drug　delivery,　and　magnetically　responsive　photonic　crystals.