Attention-deficit/hyperactivity disorder (ADHD) is a disorder characterized by chronic and pervasive signs of inattention, impulsivity, and hyperactivity. Research has indicated that the disorder is multifactorial and involves a combination of genetic inheritance and environmental factors. Evidence from twin studies suggests that genetics plays a significant role in the development of the disorder. Recent research has also identified various central nervous system abnormalities in individuals with ADHD, further confirming the neurobiological basis of the disorder. While the exact causes of ADHD are still unknown, it is widely accepted that biological factors are involved. This is supported by the complex involvement of multiple brain pathways and key neurotransmitters in the etiology of ADHD.