The d2 Test measures processing speed, rule compliance, and quality of performance, allowing for a neuropsychological estimation of individual attention and concentration performance. Originally developed to measure driving aptitude and efficiency, the d2 Test has become the mainstay of attentional assessment in Europe. The test can be administered within 8 minutes, either individually or in a group format. The economy of the test expands its availability to a much larger population of neuropsychologists, researchers, and clinicians. The reliability has proven to be very high, and the validity of the technique has been documented by a number of research studies. Extensive norms are available based on a German sampling of over 6,000 subjects. Preliminary US norms for children, college students, and the elderly are also included. Research supports the multiple clinical and empirical applications of the d2 Test. Now available for the first time with an English manual, including norms and correlations, this user-friendly test is gaining increasing recognition in the US. This test belongs in every researcher's and clinician's test repertoire, especially when the assessment of attentional capabilities has to be balanced against cost-effectiveness.