The maximal reliability of a congeneric measure is achieved by weighting item scores to form the optimal linear combination as the total score; it is never lower than the composite reliability of the measure when measurement errors are uncorrelated. The statistical method that renders maximal reliability would also lead to maximal criterion validity. Using a career satisfaction measure as an example, the present article calculated the maximal reliability and maximal criterion validity and compared them with the composite reliability and the scale criterion validity, respectively. The improvement of reliability and validity indicated that the optimal linear combination is preferred when forming a total score of a measure. The Mplus codes for analyzing maximal reliability, maximal criterion validity, and related parameters are provided.