This paper summarises the recent research on the chromogenic performance of a unique class of nanomaterials, tungsten oxide (WOx), and highlights their potential applications in energy-related areas. WOx exhibits a wealthy range of interesting chromogenic characteristics and has recently shown great potentials towards practical energy-related applications. Recent developments in nano-sized WOx synthesis have made these potentials even more appealing to engineers, bringing in immense challenges in research and equally tremendous opportunities for applications. The potential smart window/ glazing applications for energy saving, the thermochromic coating attractions in solar-thermal conversion, and the highly efficient gas-chromic applications as effective hydrogen sensors during energy generation and transportation, all point to current and future energy-related research areas and demand further efforts to achieve thorough understandings prior to materialisation. Pursuing for understandings of the relationship loop of the chemical composition-physical structure-colouration behaviour of these WOx-based nanomaterials will be first summarised. The mechanisms for different types of chromism of these materials will then be presented, and factors affecting colouration efficiencies will be analysed. The synthesis, processing and post-treatment techniques associated with their chromogenic performance will be discussed. The current technical challenges and future potentials of this unique WOx in applications will be discussed throughout the text. (C) 2017 Elsevier Ltd. All rights reserved.