We examined the association between reading and general cognitive ability (g) in a population-based sample of 6,476 pairs of 7-year-old twins. Additive genetic influences largely accounted for individual differences in reading and the covariation between reading and g. Furthermore, both genetic and shared environmental influences on reading and g correlate highly. Nonetheless, after accounting for genetic and environmental influences shared with g, there remain strong genetic and shared environmental influences specific to reading. Nonshared environmental influences are largely reading specific. There is also suggestive evidence that reading may have a causal effect on g. The results support an emerging consensus that individual differences in reading are likely to reflect genes that contribute to variation in other complex abilities reflected by g ("generalist genes"), as well as genes and environments that influence reading independent of g.