Engineering nanocrystals with size, shape, composition, structure and strain control is the key to enhance the performance of energy conversion and storage devices. In this talk, I will focus on my recent developments in rational design and controlled synthesis of high-quality multicomponent nanocrystals for fuel cells, battery and sensors. I will start with five examples on how to engineer FePt nanowires (NWs), Pd/FePt core/shell NWs, high-index faceted NiPt and CoPt alloy NWs and graphene-FePt nanoparticles (NPs) composite for achieving efficient Pt-based catalysts for oxygen reduction reaction (ORR) with extremely high activity and stability. After that, I will move to non-Pt catalysts such as graphene-Co/CoO NPs, three-dimensional (3D) ordered carbon-Co NPs, M/CuPd NPs (M=Ag, Au) and bamboo-like carbon nanotube/Fe3C NPs hybrids, which exhibit comparable and even much higher ORR activity and stability than commercial Pt catalyst. Then, I will show how to engineer bimetallic and trimetallic NPs and NWs for enhancing liquid fuels electrooxidation reactions. Finally, I will report several recent important progresses on the use of new nanocrystals for enhancing lithium ion/sulfur batteries and sensors.