This entry examines how environmental impacts influence neurodevelopmental disorders through phenotypic plasticity, which is an organism’s ability to adapt to their surroundings. The brain’s extended developmental period makes it particularly susceptible to environmental factors, which can contribute to conditions like attention-deficit/hyperactivity disorder and autism spectrum disorder. Animal studies have demonstrated how various chemicals can trigger behavioral changes by mimicking these disorders. Additionally, emerging research emphasizes the role of gut-brain communication in neuropsychiatric conditions, suggesting that early environmental exposures during critical developmental periods can have lasting effects throughout life.