CDs possess several desirable properties for photoredox catalysis, including high photoluminescent quantum yields (ref , sufficiently long excited-state lifetimes (ref , tunable optical gaps (ref , and outstanding efficacy for photo-induced electron transfer processes (ref 29). In particular, CDs have shown excellent activity in photocatalytic oxygen reduction reactions (ref . Inspired by these results, we hypothesized that similar photo-induced electron transfer events could occur between CDs photoredox catalysts and hydrogen atom transfer (HAT) agents, thereby facilitating dual catalytic C-H functionalization reactions . In this study, we report the first example of C(sp 3 )-H bond functionalization catalyzed by CDs, achieving remarkable efficiency and chemical selectivity. Intriguingly, the catalytic activity and selectivity were found to depend critically on the specific CDs photocatalyst employed. Even minor compositional differences lead to dramatic change in reactivity, switching between photoinduced Giese radical addition and dehydrogenative annulation (Fig. ). Beyond the inherent economic and environmental advantages of metal-free photocatalysis, we recognize that the functional group enriched carbon surfaces of CDs offer unique opportunities for novel selectivity, distinct mechanistic pathways, and cascade transformations.