Significance Spatial ability is a strong predictor of several important outcomes, including success in science, technology, engineering, and mathematics (STEM) subjects and careers. This ability is widely believed to be multifactorial, with numerous components and subdomains, such as “mental rotation,” “scanning,” and “mechanical reasoning.” This large twin study allows the genetic and environmental etiology of diverse putative spatial abilities to be explored. The results indicate that this domain is in fact unifactorial, albeit dissociable from general intelligence, suggesting that its structure is much simpler than the sprawling literature suggests. This will aid gene-hunting efforts and allow this ability and its consequences to be examined with greater precision.