Significant limitations in research on learning disability (LD) have included failure to incorporate well-validated guiding theories, use of vague or nonspecific operational definitions, and lack of a systematic framework and common terminology for LD identification. Difficulties in communication among researchers continue to limit theoretical development and empirical advancement, and have lead to disagreement regarding best practices in identification. To this end, we propose an operational definition of LD that is grounded in contemporary psychometric theory and research on the relations between cognitive abilities/processes and academic outcomes. We demonstrate that response-to-intervention (RTI) and norm-referenced ability testing should not be viewed as mutually exclusive, but instead should be integrated within an operational definition of LD. Only when there exists a common set of definitions and terms, as is evident in operational definitions, can researchers and practitioners move toward the goal of better diagnosis and treatment of LD. (Contains 2 figures and 2 tables.)