**1. Introduction**

The recycling and reuse of solid wastes can be considered important challenges for civil and environmental applications in the frame of a more sustainable model of development and the consumption of new resources and energy [1–5]. The recovery of raw materials from nonconventional sources and their transformation into usable resources not only represents an economic advantage, but also offers an ecological opportunity for the utilization of by-products which would otherwise be landfilled [6–11]. In this respect, these secondary raw materials, generally derived from industrial, agricultural and food manufacturing activities, become an abundant resource that can be easily reused for different applications, as reported in the recent studies collected in this Special Issue.

For that purpose, six papers were related to the preparation of innovative composite materials. Specifically, five papers reported the reuse of end-of-life tire rubber, porous glass, expanded polystyrene, slags, fly ashes and sheep's wool fibers for the preparation of cement conglomerates [12–16], while the last one reported the reuse of amorphous silica nanoparticles for the preparation of composites with natural rubber [17]. Moreover, five papers were related to the treatment of wastes for environmental applications. Specifically, two papers reported the reuse of egg by-products [18] and crab shell [19] for the removal of biopersistent micropollutants, and two papers reported the reuse of white bamboo fibrils as oil absorbent [20] and a rapid method for the disposal of radioactive contaminated soil waste [21], respectively. The last one reported the use of wheat straw biochar for cobalt sorption from contaminated soil [22].
