For decades, metal oxides have attracted interest because of the versatility of the methods for their obtaining, which allow the formation of nanomaterials with novel and improved properties than their bulk counterparts. Metal oxide nanomaterials have wide applications because of they are easy to combine, functionalize and dope with organic or metal moieties. During the last decade the potential of metal oxide nanomaterials for addressing environmental and biological issues has significantly increased extending their applications in almost all the areas demonstrating their potential for its incorporation as part of new technologies. The topics approached in this special issue, are focused on applications for metal oxide nanomaterials alone or in combination with other materials, related to environmental remediation such as heterogeneous photocatalysis for the removal of water pollutants or hydrogen production, catalysts for biofuels obtaining, electrocatalysis, antimicrobial and antifungal agents among others. The novelty and impact of the synthesis methods and its relationship with their properties will be considered too.