An information-processing assessment of the construct validity of aptitude tests is presented. It is stated that aptitude tests have been rather successful because they possess high construct validity, although the constructs in terms of which the tests may be most profitably understood are information-processing rather than psychometric ones. It is suggested that certain inconsistencies in the constructs proposed by alternative psychometric theories of aptitude tend to disappear when these constructs are understood in terms of more basic information-processing constructs. Several theories are discussed: componential theory; Spearman's two-factor theory; Thurstone's primary mental abilities; Cattell and Horn's fluid and crystallized ability; and Guilford's structure of intellect. (Author/GDC)