In recent years, single-atom catalysts attracted lots of attention because of their high catalytic activity, selectivity, stability, maximum atom utilization, exceptional performance, and low cost. Single-atom catalyst contains isolated individual atom which are coordinated with the surface atoms of support such as a metal oxide or 2d - materials. In this review article, we present the advancement in single-atom catalysis in recent years with a focus on the various synthesis methods and their application in catalytic reactions. We also demonstrate the reaction mechanism of a single-atom catalyst for different catalytic reactions from theoretical aspects using density functional theory.