The polychlorinated compounds discussed in this chapter are man-made chemicals, including polychlorinated biphenyls and polychlorinated naphthalenes, that have been used for decades in various open and closed applications, such as lubricants, gear oils, flame retardants for wood, paper, fabrics, leather, coatings, and additives in adhesives, sealants, transformers, condensers, and hydraulic fluids. Conversely, polychlorinated and polybrominated dibenzodioxins and dibenzofurans come from anthropogenic sources and are unintentionally generated as byproducts of various industrial, chemical, and incomplete thermal processes. Overall, these substances are prevalent in the environment and humans and face restrictions due to their persistence and toxicological properties, as outlined in the Stockholm Convention on Persistent Organic Pollutants. Therefore, this text provides a brief description of the chemical-physical characteristics, use patterns, primary health risks, and toxicokinetic properties of these substances, as well as references for further scientific literature. The primary objective is to detail their occurrence in human matrices, such as blood, urine, and breast milk. To this end, comprehensive information is presented on polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins/furans (PCDD/PCDFs), dioxin-like PCBs, polybrominated dibenzodioxins/furans (PBDD/PBDFs), and polychlorinated naphthalenes (PCNs).