The current study examines the Strong Interest Inventory's (SII) ability to measure vocational interests and better understand how it predicts concurrent undergraduate academic majors. Although much literature exists concerning vocational interest measurement, no published study has utilized all scales on the SII to predict concurrent academic majors while also exploring the extent of the congruence-achievement hypothesis on undergraduate students. Furthermore, no previous empirical investigations have explored the way classification hit rate percentages were calculated or identified the rank of the matched Occupational Scales (OSs) on the SII. The concurrent validity of the SII was tested by (a) examining hit rates for the OSs in predicting college major choice utilizing the McArthur method (N = 100 females and 100 males); and (b) analyzing which scales (i.e., General Occupational Themes [GOTs], Basic Interest Scales [BISs], Personal Style Scales [PSSs]) on the SII are more effective at differentiating and predicting concurrent college majors (N=501). The congruence-achievement hypothesis was tested by quantifying the amount of congruence between participants' Holland personality types and the types associated with their declared academic majors, and how well this congruence predicts level of achievement (i.e., GPA). Findings supported the ability of the SII to accurately predict concurrent majors at the undergraduate level. Specifically, the first hypothesis, which stated that the OSs of the SII will predict a participant's exact academic major (i.e., Direct Excellent Hit) for at least 35% of the sample, was supported. The second hypothesis, which predicted that the BISs of the SII will show the highest level of accuracy in predicting participant academic majors followed by the GOTs and PSSs, was also supported. Finally, the last hypothesis, which predicted that greater congruence between individuals' GOT scores and their academic majors will be associated with greater cumulative GPAs, was not supported. Strengths, limitations and future directions are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]