People’s concept of free will is often assumed to be incompatible with the deterministic, scientific model of the universe. Indeed, many scholars treat the folk concept of free will as assuming a special form of nondeterministic causation, possibly the notion of uncaused causes. However, little work to date has directly probed individuals’ beliefs about what it means to have free will. The present studies sought to reconstruct this folk concept of free will by asking people to define the concept (Study 1) and by confronting them with a neuroscientific claim that free will is an illusion (Study 2), which invited them to either reconcile or contrast free will with determinism. The results suggest that the core of people’s concept of free will is a choice that fulfills one’s desires and is free from internal or external constraints. No evidence was found for metaphysical assumptions about dualism or indeterminism.