The mind-blindness theory of autism spectrum conditions has been successful in explaining the social and communication difficulties that characterize these conditions but cannot explain the nonsocial features (the narrow interests, need for sameness, and attention to detail). A new theory, the empathizing–systemizing (E-S) theory, is summarized, which argues two factors are needed to explain the social and nonsocial features of the condition. This is related to other cognitive theories such as the weak central coherence theory and the executive dysfunction theory. The E-S theory is also extended to the extreme male brain theory as a way of understanding the biased sex ratio in autism. Etiological predictions are discussed, as are the clinical applications arising from the E-S theory.