Reading disability shows substantial genetic influence, and it is in this area of early-onset cognitive delays that genetic research has made the most progress. Reading disability also provides the first success story for identifying replicable quantitative trait locus linkage for behavioral disorders. Language and communication disorders also show substantial genetic influence, as does general cognitive ability (intelligence), which plays a role in most cognitive disabilities. The genetics of reading disability, communication disorders, and mental retardation are reviewed. Early-onset cognitive disabilities are prime targets for molecular genetic studies that will eventually identify specific genes that can predict risk, assist diagnosis and treatment, and provide discrete windows through which we can investigate the development of brain mechanisms that lie between genes and behavior.