Cobalt oxide nanostructures have been considered as promising electrode materials for various electrochemical applications, especially for batteries, supercapacitors, and electrocatalysis, owing to their unparalleled advantages of high theoretical capacity, highly-active catalytic properties, and outstanding thermal/chemical stability. If hybridized with property-complementary nanomaterials, such as nanocarbon, CNTs, graphene, metal oxides/sulfides and conductive polymers, their electrochemical properties can be further enhanced in terms of specific reversible capacity/capacitance, rate capability, cycling stability, and catalytic activity. In this review, we first give a comprehensive overview on recent progress in both monolithic cobalt oxide nanostructures and their hybrid nanomaterials for batteries, supercapacitors, and electrocatalysis applications. Then, structure-property relationships of the cobalt oxide-based nano materials and current challenges in both nanoarchitectures design and their applications in electrochemical energy devices are proposed, and an outlook on future research of this family of materials in electrochemical energy applications are brought forward. This understanding on the relationships of synthesis-nano/microstructure-property-performance of cobalt oxide-based nanomaterials is expected to lay a good foundation for pushing this promising class of materials to the practical application in energy conversion and storage devices and to provide a good reference for the readers in the fields of materials, chemistry, sustainable energy, and nano technology.