Rates of participation in organ donation programs are known to be powerfully influenced by the relevant default policy in effect ("opt-in" vs. "opt-out"). Three studies provide evidence that this difference in participation may occur in part because the requirement to opt-in or opt-out results in large differences in the meaning that individuals attach to participation. American participants in Study 1 rated participation as a significantly more substantial action when agreement was purportedly obtained under opt-in rather than opt-out conditions, and nonagreement as a greater abrogation of responsibility when that decision was made under opt-out rather than under opt-in conditions. Study 2 replicated these findings with respondents who live in Germany, which employs an opt-in donation policy, and in Austria, which has an opt-out policy. Study 3 required American participants to rate various actions that differ in the effort and self-sacrifice they demand. As predicted, the placement of organ donation on the resulting multidimensional scaling dimension differed significantly depending on whether it purportedly was made in an opt-in country (where it was considered roughly akin to giving away half of one's wealth to charity upon one's death) or an opt-out country (where it fell between letting others get ahead of one in line and volunteering some time to help the poor). We discuss the relationship between this change of meaning account and two other mechanisms-behavioral inertia and implicit norms-that we believe underlie the default effect in decision making and other effects of policies designed to influence decision-makers.