Although it is well established that experience seeking behavior (ES) is positively related to cognitive functioning, the mechanisms underlying this association are not clearly understood. In a large sample of adult twins and siblings (N = 864, age range 23–75), we studied the causes of covariation between ES and general cognitive ability and we studied whether ES moderates the genetic and environmental causes of variation in general cognitive ability. Results demonstrate a phenotypic correlation of .17 (p <.001) between general cognitive ability and ES, with a common genetic and common environmental background. Moreover, the extent to which genetic and environmental factors are shared between general cognitive ability and ES is increased in individuals with either lower or higher levels of ES. In addition, the extent to which genetic and environmental factors influence individual differences in general cognitive ability in adults partly depended on ES. Standardized influences of additive genetic factors on general cognitive ability ranged from 13% to 99%, with lower estimates in higher levels of ES, while standardized estimates of environmental factors ranged from almost 1% to 87%, with higher estimates in higher levels of ES. Hence, ES and cognitive ability are not only associated through common genetic and environmental factors, but also via moderating effects of genetic and environmental influences on cognitive ability by ES. These findings have implications for future studies on the association between ES and general cognitive ability, and for future research on the genetics of cognitive ability.