Many behavioral scientists argue that assessments used in social indicators research must be content-valid. However, the concept of content validity has been controversial since its inception. The current unitary conceptualization of validity argues against use of the term content validity, but stresses the importance of content representation in the instrument construction and evaluation processes. However, by arguing against use of this term, the importance of demonstrating content representativeness has been severely undermined. This paper reviews the history of content validity theory to underscore its importance in evaluating construct validity. It is concluded that although measures cannot be “validated” based on content validity evidence alone, demonstration of content validity is a fundamental requirement of all assessment instruments.