This book is the manual to the d2 test, a psychodiagnostic instrument for measuring processing speed, rule compliance, and quality of performance, allowing for a neuropsychological estimation of individual attention and concentration performance. The German version of this detail discrimination test has in recent years become tremendously popular because of its extremely high reliability, validity and economy of use. Originally developed to assess suitability for driving, the test has also been used extensively as a part of personnel selection in many other workplace environments where high levels of visual attention and concentration are demanded, including, for instance, selection of pilots by airlines. In recent years it has also found increasing application in other areas, such as clinical, educational and developmental psychology, and even psychopharmacology, as well as less clinical settings such as vocational counselling, industrial psychology, sports psychology, and driver psychology. The test is virtually language independent, can be performed individually or in a group, and takes only eight minutes including the instructions and the administration, and since its inception the test has undergone frequent revisions and translations, reflecting continuing efforts to insure its empirical and clinical suitability, and extend its use. Extensive norms are available based on a German sampling of over 6,000 subjects, and this manual includes preliminary US norms for children, college students, and the elderly.