Most advanced societies, today, are committed to the principle of equal rights for men and women. In Britain, legislation is on the statute books with regard to equal pay and for the removal of unfair discrimination. Ideally, this legislation should be based on and supported by a full understanding of the relative abilities of men and women, so that it is just and can be operated with complete appreciation of its limitations and consequences. Unfortunately, few researchers have been willing to tackle questions of sex differences in ability, the general view being that any differences which exist must be the product of an unjust social system and that, if differences can be proven, this will only justify existing prejudices. This paper challenges these views. It argues that there are some differences between men and women which have serious implications for employment and that, rather than defeating the cause of sexual equality, an understanding of them is essential to its success.