Both criterion-referenced testing and behavioral assessment share the basic assumption that test behavior is a sample rather than a sign. In addition, both types of assessment focus on response capabilities and performance in specified content domains. Although content validity has been traditionally recognized as essential to criterion-referenced testing, it has not been as generally recognized as relevant to behavioral assessment. The relationship between the two types of assessment clarifies the importance of content validity for behavioral assessment. Questions of content validity can be usefully conceptualized from the point of view of generalizability theory. The relevant question then becomes: Are the test items a representative sample of the universe to which results are going to be generalized? Finally, content validity is as important in assessment procedures developed on an idiographic level as it is in those developed nomothetically. (Author/CTM)