Fly ash cenospheres (FACs) are among the most valuable by-products obtained from the burning of coal. They are lightweight (density 400-800kg/m), hollow, and spherical in nature, and hence find useful industrial applications. Due to their excellent inherent properties, such as superior mechanical strength, low bulk density, high thermal resistance, and low cost, they are environmentally viable materials for various applications. FACs used in different composites, such as ceramics, geopolymers, concrete, mortars, etc. may reduce environmental burden, thus promoting sustainable development. In this chapter, FAC formation, characterization, processing (including the chemical composition, their recovery from fly ash), and properties have been discussed in detail.