Oxide nanostructures in low dimensions on well-defined metal surfaces form novel hybrid systems with tremendous potential and impact in fundamental research and for the emerging nanotechnologies. In contrast to bulk materials low-dimensional oxide nanostructures not only involve a large number of undercoordinated atoms but their interaction with the metal substrate also provides constraints on their structure and morphology and often yields elastic strain and/or uncompensated charge. These factors modify significantly the physical and chemical properties of the nanophases as compared to bulk oxides. In this review the authors will examine critically the available data with respect to structure-property relationships of metal-supported oxide nanostructures in reduced dimensions. The connection between structure, elastic strain, and charge transfer on the one hand, and electronic and magnetic behavior on the other one, will be discussed. The novel chemical properties of the oxide-metal nanostructure systems will provide another focus of this review.