In order to take advantage of advances in the field of mental measurement, the Armed Forces and the Department of Defense have supported the development of a computerized adaptive version of the Armed Services Vocational Aptitude Battery (ASVAB) for use in military personnel selection and classification. This report describes the development and calibration of item pools for each of nine ASVAB content areas. Domain specifications were developed for the content areas, and more than 3,600 items were written. The items were then pretested on samples of recruits. These data were used to select items for calibration in a sample of over 138,000 examinees tested in Military Entrance Processing Stations and their associated testing sites in May and June of 1983. The calibration data were then analyzed using both an equivalent-groups design and a joint-calibration design that used matched experimental and operational test data. Item response theory a, b, and c parameters based on the three-parameter logistic item response model were computed. The parameters resulting from the joint-calibration approach were recommended for operational use. (Author)