Cenospheres are one of the most value added fractions of coal fly ash. They have a hollow spherical structure and can be applied in many industrial applications, due to their superior properties; such as low bulk density, high thermal resistance, high workability and high strength. This review, focuses on the formation of cenospheres, their characterisation, including the chemical composition, their recovery from fly ash and the influence on mechanical properties when mixed with different materials. (C) 2017 Elsevier Ltd. All rights reserved.