This chapter presents the beginnings of vocational interest measurement and the subsequent refinements of measures focusing in depth on several seminal measures. It discusses general trends but also concentrate on several key figures. Strong’s original inventory was named Strong’s Vocational Interest Blank, and then changed to Strong-Campbell Interest Inventory. Responses of reference groups and that of men-in-general, or women-in-general, were compared. Then based on how large differences were between these two groups, items were selected or assigned different weights on the scoring scale for that occupation. The average odd-even reliability coefficient of 36 revised scales was 0.88 for 285 Stanford senior males, with only one scale falling below 0.80. In the 1968 revision, the first group of homogeneous content scales, Basic Interest Scales, were added to the Strong Interest Inventory. Themes showed predictive validity nearly as high as the Occupational Scales for males, with direct and indirect good hits at the rate of 31% to 69%.