Supercapacitors are promising energy storage and conversion devices with high power densities. However, their low energy densities limit their practical application. The electrode is a key component that determines the performance of supercapacitors. As electrode materials, transition metal oxides/hydroxides usually exhibit high capacitance, leading to high energy densities. This review discusses the advantages and disadvantages of different metal oxides/hydroxides, in order to synthesize high-performance electrode materials. Two main strategies to enhance the supercapacitive performance are proposed: developing composites and nanostructured materials.