Display omitted •The up-to-date reports with respect to the chemical synthesis of SAA are overviewed.•The significance of SAA for representative electrochemical and heterogeneous catalytic reactions is analyzed.•The major challenges and opportunities pertaining to this cutting-edge field are suggested. The development of low-cost, high-performance catalysts at the atomic level has become a challenging issue for large-scale applications of renewable clean energy technologies. Atomic sites catalysts, such as single atoms catalysts (SAC), single clusters catalysts (SCC), single-atom alloys (SAA), have proved their performance in various catalytic reactions due to their extremely high atom utilization efficiency, unique structure, and exceptional catalytic selectivity. A deep understanding and design of the active center of the catalyst at the atomic level has become a top priority for current research. Compared with SAC and SCC, SAA has its own uniqueness. In this review, we focused on the recent progress on the preparation methods of SAA and discussed the key factors controlling the structure of SAA. In addition, several important catalytic reactions performed over well-defined SAA are analyzed. Finally, the challenges and the perspectives of this cutting-edge field are suggested. We believe that this critical review provides a guidance for the rational design of SAA for catalytic applications.