Activated carbons (ACs) have been used in bygone years in environmental applications because of their high efficiency in many remediation and degradation processes. Due to their many desirable properties, such as chemical stability, inertness, mechanical resistance, high surface area, porosity, low cost, and availability, ACs have been explored as auxiliary materials in many new catalysis applications employing new process intensification technologies, or in the form of composites. In this chapter, AC's state of the art is explored while discussing the main methods for its production from several distinct carbon sources. The effects of AC in environmental remediation catalysis assisted by microwave and ultrasound methods are presented, and the mechanisms behind the synergistic effects occurring in these processes are discussed. In sequence, the synthesis and preparation of novel AC composites and their application in the removal of emerging pollutants such as pharmaceuticals and personal care products (PPCPs), pesticides, microplastics, and endocrine disruptors are presented in detail, unveiling the ultimate key role and relevance of AC in 21st-century environmental catalysis.