This article provides a brief overview of the various areas of research that have served to clarify the condition of dyslexia. Using topics and content appearing in A. L. Benton and D. Pearl's (1978) text, Dyslexia: An Appraisal of Current Knowledge, as the point of departure, evolution of the definitions of dyslexia is traced to the current and widely held understanding of this learning disability as specifically related to a deficit in phonological processing abilities. The most prominent competing hypothesis--that a naming-speed deficit might also account for dyslexia--is also discussed. Research in the areas of human genetics, perceptual processing, and brain structure and function is summarized, as these have contributed to our current understanding of how dyslexia affects one's ability to read. The article concludes with a discussion of how dyslexia is manifested in languages other than English, as well as how research to date has influenced approaches to assessment and instruction.