Controlled creation of intrinsic defects such as oxygen vacancies can effectively modulate the optical and electronic properties of metal oxide nanomaterials. In the past few years, a number of oxygen defective metal oxides have been developed and implemented as electrode materials for energy conversion and storage applications. They show significantly enhanced performance for photoelectrochemical water splitting, electrochemical charge storage, and (photo) electrochemical catalysis. In this review, we present an overview of progress made in preparing oxygen defective metal oxide nanostructures and probing the role of oxygen vacancies on the performance of metal oxides, and identify the key challenges and future opportunities for oxygen defective metal oxides. (C) 2017 Elsevier Ltd. All rights reserved.