From early in development children show impressive knowledge about mental states such as beliefs and desires. However, less is known about the development of knowledge about more sophisticated aspects of mental activity, including the adult intuition that the mind is an independent agent over which we have some but not total control. This project explored 8- to 11-year-olds’ (n = 46) and adults’ (n = 48) beliefs about the extent to which thoughts, emotions, and behaviors are controllable. Results indicated that both children and adults viewed thoughts and emotions (in contrast to behavior) as relatively involuntary. Children and adults also generally rejected the notion that mental activities and behaviors are chronic. However, while adults were skeptical about whether people can stop their own thoughts, emotions, and behavior, children fully endorsed this type of control. Overall, data suggest that intuitions about the controllability of mental activities continue to mature throughout childhood.