AbstractElectrocatalytic carbon dioxide reduction reaction (CO₂RR) holds significant potential to promote carbon neutrality. However, the selectivity toward multicarbon products in CO₂RR is still too low to meet practical applications. Here the authors report the delicate synthesis of three kinds of Ag–Cu Janus nanostructures with {100} facets (JNS‐100) for highly selective tandem electrocatalytic reduction of CO₂ to multicarbon products. By controlling the surfactant and reduction kinetics of Cu precursor, the confined growth of Cu with {100} facets on one of the six equal faces of Ag nanocubes is realized. Compared with Cu nanocubes, Ag₆₅–Cu₃₅ JNS‐100 demonstrates much superior selectivity for both ethylene and multicarbon products in CO₂RR at less negative potentials. Density functional theory calculations reveal that the compensating electronic structure and carbon monoxide spillover in Ag₆₅–Cu₃₅ JNS‐100 contribute to the enhanced CO₂RR performance. This study provides an effective strategy to design advanced tandem catalysts toward the extensive application of CO₂RR.