Polychlorinated biphenyls (PCBs) are pervasive environmental pollutants. Despite having been banned from production in 1979 by the USA and most parts of the world since the early 2000s, PCBs continue to pose a significant risk to human health. Humans are exposed via diet and inhalation to not only legacy PCBs from commercial mixtures synthesized prior to the ban on PCB production, but also PCBs created as inadvertent byproducts of contemporary manufacturing processes. A major target of concern for PCBs is the developing brain; however, adverse effects on the adult and aging brain have also been reported. In this chapter, we summarize epidemiological and experimental animal studies of early-life and mid-life exposures to PCBs, focusing on outcomes across domains related to cognition (e.g., IQ, language, memory, learning), attention, behavioral regulation and executive function, and social behavior, as well as traits related to attention deficit hyperactivity disorder (ADHD), autism spectrum disorders (ASD), affective disorders, and neurodegenerative diseases.