The ways in which women and men differ in intelligence and specific cognitive abilities are among psychology’s most heated controversies. Massive amounts of data show that although there are some on average differences in specific cognitive abilities, there is considerable overlap in the male and female distributions. There are no sex differences in general intelligence – standardized IQ tests were written to show no differences, and separate assessments that were not written with this criterion show no differences in general intelligence. There are more males in some categories of mental disability that are genetically linked, but there are no genetic explanations for differential achievement at the high end of the distributions. Average between-sex differences on specific cognitive abilities – notably reading and writing (female advantage) and some mathematical and visuospatial abilities (male advantage) – often show considerable cross-cultural variation in effect size. Additionally, there have been changes over time so that any conclusions about this controversial topic that we make today may need to be revised in the future.