Selectively approaching chemicals with one composition-tunable catalyst is attractive for practical manufacturing. Bimetallic copper-indium (Cu-In) catalysts have been synthesized by using a coprecipitation method and found to be among the best reported In-based catalysts for electrochemical CO2 reduction to CO or HCOOH. By varying the metal ratio, the catalyst can be tuned from a core-shell structure that selectively produces CO to a well-mixed structure that prefers HCOOH production. The distinct selectivities depend on the structure-sensitive binding strength of key reactive intermediates. These findings can benefit the development of a broader range of selectivity-tunable catalysts.