This chapter describes the four main evolutionary stages that have marked the history of military selection and classification psychological testing in the United States. These progressive stages have corresponded to the advancing complexity of the challenges the military has faced. The first stage, stimulated by the unprecedented requirements for manpower in World War I, involved the development of group standardized screening tools, the Army Alpha and Beta. With World War II came the second stage, the first classification tools to match enlistees to jobs. The third stage, coincident with the transformation of the military to the All-Volunteer Force, involved coordination of selection and classification processes across all the military services and the development of the joint-service Armed Services Vocational Aptitude Battery (ASVAB). Today, in a world of highly diverse military missions, the fourth evolutionary stage is being experienced, in which cognitive testing is being supplemented by non cognitive measures, including personality and interest tests.