This report examines the construct validity of the Ball Aptitude Battery (BAB), a multiple ability test battery designed to measure aptitudes related to successful work behavior. Construct validation has focused attention on the role of psychological theory and on the need to formulate hypotheses that can be examined in the validation process. Evidence of construct validity arises from several sources, and this paper summarizes existing evidence from concurrent validation and factor analytic studies of the BAB. A multimethod-multitrait approach comparing the BAB with the Comprehensive Ability Battery and the Differential Aptitude Tests is reported. Each test from the three batteries was classified into one of 10 aptitude constructs derived from a previous BAB factor analysis: Grip, Finger Dexterity, Spatial, Inductive Reasoning, Analytical Reasoning, Vocabulary, Word Association, Fluency, Writing Speed, and Clerical. Correlations showed clear evidence of discriminant and convergent validity for most of the BAB aptitudes. (Author/BS)