The progress on synthesis of colloidal nanocrystals (NCs) has enabled researchers to engineer crystalline nanoparticles over many aspects including composition, size, morphology, crystal structure, surface functionalities, and so on. The rendering unique chemical and physical properties of these precisely engineered colloidal NCs make them superior to their bulk counterparts in many applications, especially for electrochemical reduction reactions that are currently extensively investigated to resolve global energy and environmental issues. Herein we present the recent progress of colloidal NCs and their roles in electrochemical reduction reactions, such as oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO2RR). In this feature article, we first introduce the colloidal NCs on the synthesis of colloidal NCs with controlled size, shape, composition and structure. We then focus on the emerging concept in colloidal NCs synthesis, as well as the self-assembly of colloidal NCs to superlattice structures. Afterwards, we discuss the fundamentals and representative strategies in designing colloidal NC structures for superior catalytic performance in ORR, HER and CO2RR. In the end, we provide a perspective on the future opportunities of colloidal NCs in electrochemical reduction reaction applications. (C) 2016 Elsevier Inc. All rights reserved.