The front cover picture shows a distinct size-dependent affinity of gold (Au)-based materials for dioxygen (O₂). Although Au is chemically inert against O₂, unique reactivities emerged at the nanometer to the atomic scales. Atomically precise Au nanoclusters and molecular Au complexes with supporting ligands exhibit affinity for O₂, and detailed mechanisms for O₂-activation by these Au-based nanomaterials can be revealed on the basis of both experimental and theoretical analyses. More details can be found in the Concept by Wataru Suzuki and Toshiharu Teranishi (DOI: 10.1002/cplu.202500244).