The chapter "Understanding the Dynamic Aggregation in Single-Atom Catalysis" by Laihao Liu, Tiankai Chen, and Zhongxin Chen explores the dynamic response of single-atom catalysts (SACs) to reactive environments, focusing on the mechanisms and factors that drive their aggregation. The authors highlight the importance of understanding the dynamic profile of SACs during reactions, including intrinsic stability, site migration barriers, external stimuli, and catalyst support effects. They discuss how dynamic aggregation can be beneficial or detrimental to catalytic performance, depending on the initial state. The chapter also reviews operando techniques for monitoring structural evolution and emerging strategies for regulating dynamic aggregation through nano-confinement and defect-engineering. The authors emphasize the need to consider the structural dynamism of SACs in various catalytic reactions and provide examples where in situ-formed clusters serve as more active sites than single atoms. Finally, they discuss the influence of catalyst support on SAC stability and the role of multimetallic and multinuclear systems in catalysis.The chapter "Understanding the Dynamic Aggregation in Single-Atom Catalysis" by Laihao Liu, Tiankai Chen, and Zhongxin Chen explores the dynamic response of single-atom catalysts (SACs) to reactive environments, focusing on the mechanisms and factors that drive their aggregation. The authors highlight the importance of understanding the dynamic profile of SACs during reactions, including intrinsic stability, site migration barriers, external stimuli, and catalyst support effects. They discuss how dynamic aggregation can be beneficial or detrimental to catalytic performance, depending on the initial state. The chapter also reviews operando techniques for monitoring structural evolution and emerging strategies for regulating dynamic aggregation through nano-confinement and defect-engineering. The authors emphasize the need to consider the structural dynamism of SACs in various catalytic reactions and provide examples where in situ-formed clusters serve as more active sites than single atoms. Finally, they discuss the influence of catalyst support on SAC stability and the role of multimetallic and multinuclear systems in catalysis.