Purpose: To examine the etiology of the relationship between preschool speech and language, and later reading skills. Method: One thousand six hundred seventy-two children from the Twins Early Development Study (B. R. Oliver & R. Plomin, 2007) were given a comprehensive speech and language assessment at 4 1/2 years. Reading was assessed at 7, 9, and 10 years. Twin analyses were applied to the data to assess the contributions of genetic and environmental factors to the longitudinal relationships between speech and reading, and language and reading. Results: Phenotypically, there is a moderate and stable relationship between 4 1/2-year speech and language scores and reading at 7, 9, and 10 years. Etiologically, at the individual-differences level, both genetic and shared environmental factors contribute to the links between language skills and reading. By contrast, genetic factors account for most of the relationship between early speech and later reading. At the extremes, there appears to be an even stronger role for genetic factors in accounting for the prediction from early speech and language impairments to later reading outcome. Conclusion: Both genetic and environmental factors contribute to the relationship between early language skills and reading, whereas genetic factors play a dominant role in the relationship between early speech and reading.