This work summarizes the use of graphene/Co3O4 composites in electrochemical energy conversion and storage applications. Graphene is considered the most promising carbon material for accommodating multifarious nanoparticles and achieving excellent electrochemical performance, such as a high electrolyte contact area, electron transport rate and structural stability. This work presents different nanostructures of Co3O4 that consist of nanowires, nanotubes and ordered mesoporous structures, many of which have been poorly synthesized by facile strategies. Graphene can effectively house Co3O4 nanoparticles inside its 3D structure and greatly enhance the electrochemical performance of these nanoparticles. The synergistic effects of graphene and Co3O4 lead to a variety of attractive properties, such as excellent reversible capacity and good cycling stability. In addition, these unique properties are due to the many short diffusion pathways and active sites of nanosized Co3O4 and the elastic buffer space and conductive pathways provided by graphene. This comprehensive review outlines the excellent electrochemical performance of graphene/Co3O4 composites in electrocatalysis, supercapacitors, lithium-ion batteries and other batteries.