Attention Deficit Hyperactivity Disorder (ADHD) is a relatively common disorder that affects around 3 in 100 children. Although it first starts in childhood, problems can persist into adult life. Despite enormous advances in research, it remains poorly understand and regularly continues to attract controversy.What is ADHD? Why is it not simply "naughty behaviour"? What we have learnt about causes? My aim is to consider myths and misunderstandings. I will focus on has been learnt from science, and how this might help clinical and educational practice.