Copper-catalyzed halide exchange reactions under very mild reaction conditions are described for the first time using a family of model aryl halide substrates. All combinations of halide exchange (I, Br, Cl, F) are observed using catalytic amounts of Cu-I. Strikingly, quantitative fluorination of aryl X substrates is also achieved catalytically at room temperature, using common F- sources, via the intermediacy of aryl-Cu-III-X species. Experimental and computational data support a redox Cu-I/Cu-III catalytic cycle involving aryl X oxidative addition at the Cu-I center, followed by halide exchange and reductive elimination steps. Additionally, defluorination of the aryl-F model system can be also achieved with Cu-I at room temperature operating under a Cu-I/Cu-III redox pair.