The Special Issue "Recycled Materials in Civil Engineering Application" aims to discuss the preparation and characterization of new ecologically friendly materials containing recycled materials or waste that could be used in specific engineering applications. Using waste and materials obtained through recycling is a key part of decreasing current waste. In concrete and other composite materials, recycled materials such as plastics, steel and other metals, ash, glass, ceramics, and industrial wastes see the most use. The application of recycled materials or waste to the production of new materials is consistent with the idea of sustainable construction. Using recycled materials to synthesize composite materials saves the use of natural resources and has a positive influence on environmental protection. Unfortunately, the production of composite materials containing waste, by-products, or recycled materials requires a substantial amount of research, and is a very relevant issue for materials engineers and chemists. For this reason, in this Special Issue we publish the latest research results in the field of the synthesis of composite materials, in particular cement-based composites and their physicochemical and mechanical properties, as well as their impact on the natural environment.