The development of high-performance electrocatalysts is critical for the widespread applications of the sustainable energy technologies. In this context, single-atom catalysts (SACs) with isolated metal sites have attracted more attention because of their maximum atom utilization and remarkable electrocatalytic performance. However, the high surface energy often results in a low loading of the single metal atoms, limiting their practical applications. Herein, we give an up-to-date review on the progress for the SACs. The research progress of noble metal SACs, transition metal SACs, single-atom alloy SACs, and double metal SACs is summarized. The advantages and disadvantages of synthesis strategies including wet chemistry, atomic layer deposition, and high-temperature pyrolysis are discussed. We also propose some new research direction to obtain the high-performance SACs. It is expected to realize widely applications of SACs.