Bimetallic nanoparticles with dilute alloyed surfaces are promising materials for many applications, especially catalysis. However, the preparation of nanoparticles composed of catalytically advantageous metal pairs is complicated by challenges, such as lattice mismatch and dissimilar reduction potentials. Herein we outline several particle systems that produce unique mono and bimetallic structures that are catalytically relevant. Moreover, the work outlined in the final chapter describes a novel application for halide ions within bimetallic systems. Indeed, low concentrations of halide ions provide a knob by which metal ion reduction may be differentially tuned in one-pot syntheses at mild temperatures. Additionally, this differential control has been shown effective in multiple metal systems including gold and palladium, palladium and copper, and gold and silver suggesting that these findings have the potential to be generally applicable. Differential metal ion reduction provides an avenue for the deliberate design of tunable bimetallic catalysts.