This long awaited work surveys and summarizes the results of more than seventy years of investigation, by factor analysis, of a variety of cognitive abilities, with particular attention to language, thinking, memory, visual and auditory perception, creativity and the production of ideas, and the speed and accuracy of mental processing. The author describes his detailed findings resulting from reanalysis of more than 460 data sets from the factor-analytic literature, followed by a presentation of a hierarchical, three-stratum theory of cognitive ability and its implications for further research. A set of three computer disks (IBM 3-½ 1.4 megabytes, ASCII format) containing the numerical data sets and Dr. Carroll’s statistical results is also available. Representing over 4 megabytes of data or roughly 2000 printed pages the disks are major resources for the interested researcher.