The concept of aptitude and the predictive value of aptitude patterns were fully discussed in this paper. To illustrate the importance of studies on aptitudes, the views of several prominant scholars such as Super, Biugham, and others were introduced. The author also discussed the development and application of aptitude tests. The use of High School Comprehensive Aptitude Test Battery, a battery developed by the author and C. W. Hsu, in schools in Taiwan well demonstrated the possible contribution of such tests to guidance and counseling programs. The need of more aptitude tests to gear with the Human Resource Actualization Policy was stressed.