My diploma thesis is about the topic attention-deficit/hyperactivity disorder, briefly ADHD. ADHD is one of the most common mental disorders in childhood and adolescense. In addition, this disorder persists at approximately 60 percent into adulthood. At the beginning of my thesis i focus on the definition of this disorder as well as epidemiology. It is given a brief introduction into the anatomy and pathophysiology of the nervous system. Subsequently, the mulitfactorial genesis as well as the symptomatology and classification were disscused. Moreover, the development of ADHD is described from infants to adults, an overview of comorbid disorders is given and the different procedures for diagnosis in childhood, adolescence and in adulthood were explained. Finally, I dedicate myself in the chapters therapy to the various non-drug treatment options for children, adolescents and adults such as psychoeducation, parent training, behavioral therapy and psychotherapy. In addition, in Austria registered substances for the drug-treatment of ADHD are presented as well as some substances which are used "off-label" As alternative treatment options nutrition and micronutrients, some phytopharmaceuticals, homeopathy and Bach flower therapy will be discussed.