ACCORDING TO data released by the World Health Organization (WHO), mental disorders reach about 700 million people in the world, representing 13% of all diseases. It is estimated that, currently, Attention Deficit Hyperactivity Disorder. (ADHD) affects approximately 2.5% of adults and about 3 to 7% of school-age children worldwide. Given the importance of this information, in addition to the great increase in the prevalence of the disorder among children and adults, the main objective of this book is to make a wide variety of instruments accessible (Tests, questionnaires, scales, etc.) that allow a better Evaluation of the possibility of the presence of Attention Deficit Hyperactivity Disorder (ADHD) in children, youth, and adults.