The electrocatalytic performance of Pt-bimetallic catalysts is usually limited by the lack of long-term durability, primarily due to leaching of the non-noble element under the harsh electrochemical conditions. We have recently developed cobalt-platinum core-shell nanostructures could sustain high catalytic activity for the oxygen reduction reaction, demonstrating 8 times of improvement in catalytic activity versus commercial Pt catalysts and no more than 13% of loss after 30,000 potential cycles. Furthermore, we have developed a series of core-shell nanostructures involving various transition metals, such as Co, Cu, Pd, Au, Ag, Rh and Pt. These materials have been found to exhibit superior catalytic performances in many electrochemical reactions, achieving enhanced catalytic activity and durability at reduced precious metal content. We have combined electron microscopic elemental mapping and electrochemical studies of CO stripping to follow the evolution of nanoscale and surface structures over the course of electrochemical reactions, which has allowed us to develop fundamental understanding of the interactions between the metals in the core-shell nanostructures.