Cognitive diagnostic assessment (CDA) is designed to measure specific knowledge structures and processing skills in students so as to provide information about their cognitive strengths and weaknesses. CDA is still in its infancy, but its parentage is fairly well established. In 1989, two seminal chapters in Robert Linn's Educational Measurement signaled both the escalating interest in and the need for cognitive diagnostic assessment. Samuel Messick's chapter, “Validity”, and the late Richard Snow and David Lohman's chapter, “Implications of Cognitive Psychology for Educational Measurement”, helped solidify the courtship of cognitive psychology within educational measurement. The ideas expressed in these chapters attracted many young scholars to educational measurement and persuaded other, well-established scholars to consider the potential of a relatively innovative branch of psychology, namely, cognitive psychology, for informing test development.