The existence of free will has been both an enduring presumption of Western culture and a subject for debate across disciplines for millennia. However, little empirical evidence exists to support the almost unquestioned assumption that, in general, Westerners endorse the existence of free will. The few studies that measure belief in free will have methodological problems that likely resulted in underestimating the true extent of belief. Recently, Rakos et al. (Behavior and Social Issues 17:20–39, 2008 ) found a stronger endorsement (...) of free will when demand characteristics were eliminated. The current study builds on this work by sampling incarcerated adolescents and adults, whose freedom to act is externally constrained. Belief in free will as well as attitudes toward punishment, self-esteem, and locus of control were measured. The results indicate that free will is strongly endorsed in Western society even when freedom to act is severely restricted. However, incarcerated adolescents endorsed free will to a slightly lesser extent than their nonincarcerated counterparts from Rakos et al. (Behavior and Social Issues 17:20–39, 2008 ), while incarcerated and nonincarcerated adults offered equally strong endorsements. The comparable endorsement by adults is consistent with the hypothesis that the belief in agency is an evolutionary adaptation. The small decrease found for incarcerated adolescents may reflect the interaction between developmental factors and the expression of an evolutionary adaptation. Additionally, incarcerated adolescents and adults associated beliefs in free will with viewing punishment as a means of deterrence, rehabilitation, and retribution. Incarcerated adults, but not incarcerated adolescents, associated beliefs in free will with greater self-esteem and with an external locus of control. Finally, though both incarcerated adults and adolescents endorsed free will strongly, the former manifested the belief by emphasizing free agentic choice whereas the latter focused on the personal responsibility that is interwoven with free choice. The implications of these findings are discussed in the context of evolutionary, cultural, and developmental factors. (shrink)