Atom transfer radical addition (ATRA) reactions, pioneered by Kharasch et al., increase molecular complexity through selective difunctionalization of olefins with high atom-and step-economy. When combined with visiblelight photoredox catalysis, ATRA reactions can be significantly diversified, allowing the addition of suitable precursors RX across the double bond of alkenes and alkynes. Among the various photocatalysts that were discovered to promote ATRA processes, visible-light activation of homoleptic copper(I)-phenanthroline complexes has enabled previously unknown transformations, diverted conventional reaction pathways, and fostered the invention of new catalytic modes given their ability to engage with substrates to act beyond single-electron transfer (SET) reagents. The transformation can proceed either through a Cu(I)/Cu(II) catalytic cycle involving sequential elementary steps-namely, SET, ligand exchange, and ligand transfer or a Cu(I)/Cu(II)/Cu(III) catalytic cycle involving SET-radical rebound, ligand exchange, and reductive elimination to ultimately deliver the products (Fig. ). A wide range of ATRA processes get accelerated due to the ability of Cu(II), a persistent radical, to intercept more nucleophilic transient radical species generated via the addition of R• to an alkene or alkyne. Despite these remarkable advancements, organic molecules compatible with Cu(I)-photocatalyzed ATRA processes are mainly limited to Csp 3 -X precursors (X = halides, thiocyanates etc). Cu(I)-promoted photoactivation of Csp 2 -X molecules such as aroyl chlorides to perform ATRA of alkenes or alkynes to access β-chloroacyl derivatives represents an exciting frontier for future research and development.