The classification of intelligence has been a prime interest to many for over three-quarters of a century. The Wechsler scales of intelligence and the development of factor analysis have both played major roles in the shaping of psychometric thought. An examination of this joint history by means of a review of the factor analytic studies of the Wechsler scales reveals the trends and inconsistencies in this area of mutual concern. It is now appropriate and important to bring this literature together for a united treatment as much of it is disjointed and contradictory, with many researchers remaining unaware of recent developments. The rationale for investigating the factor structure of the Wechsler scales is presented. An introduction to the number of factors problem is offered, as well as discussion of the most frequent types of analyses. Reports of changes in the factor structures are presented, and finally, new directions for future research are introduced. (Author)