Our goal in this paper is to assist state courts and legislatures as they try to carry out the task that Atkins requires of them promoting fairness and accuracy in the assessment and adjudication of mental retardation. After addressing the definition ofmental retardation in Part I, we focus on its assessment in Parts II and III, highlighting several key requirements of a scientifi-cally and clinically adequate assessment.

Part II addresses the assessment of deficits in intellectual functioning, particularly on the measurement of intelligence as represented by an intelligence quotient. Appropriate IQ tests must be used, and the scores must be interpreted in accordance with professional practice, taking into account the scores' statistical meaning, the standard error of measurement, and other factors that affect subjects' performance on these tests and the interpretations of their scores.

Part III addresses deficits in adaptive behavior, the second key component of a diagnosis of mental retardation. Adaptive behavior is difficult to measure and the scientific community's understanding of the construct is not nearly as advanced as its understanding of IQ. We offer guidance on how to operationalize theconcept of adaptive behavior and how to give it meaningful consideration in Atkins adjudications. Part IV briefly addresses the practical significance of the requirement that mental retardationbe manifest before the age of eighteen. Finally, Part V discusses the role of expert testimony and the necessary qualifications for experts testifying on the issue of mental retardation in death penalty cases.