Atomically dispersed catalysts, including single-atom, dual-atom, and periodic single-metal site catalysts, have revolutionized electrocatalysis by merging atomic precision with heterogeneous stability. This review traces their evolution from pioneering stabilization strategies to advanced microenvironment engineering, enabling breakthroughs in oxygen reduction, hydrogen evolution, and CO reduction. SACs maximize atom utilization but face multi-step reaction limits, addressed by DACs through synergistic dual-site mechanisms. PSMSCs further enhance activity via ordered atomic arrangements, ensuring uniform active sites and mechanistic clarity. Key breakthroughs include microenvironment engineering to tailor active sites, as well as advanced characterization techniques revealing dynamic restructuring under operando conditions. The transition from isolated atoms to ordered ensembles highlights the importance of atomic-level control in unlocking new catalytic mechanisms. This work underscores the transformative potential of ADCs in sustainable energy technologies and provides a roadmap for future research in rational catalyst design, dynamic behavior analysis, and scalable synthesis.