 Collective self-deception has received scant direct philosophical attention as compared with its individual counterpart. Collective self-deception might refer simply to a group of similarly self-deceived individuals or to a group-entity, such as a corporation, committee, jury or the like, that is self-deceived. These alternatives reflect two basic perspectives social epistemologists have taken on ascriptions of propositional attitudes to collectives. On the one hand, such attributions might be taken summatively as simply an indirect way of attributing those states to members of the collective (Quinton 1975/1976). This summative understanding, then, considers attitudes attributed to groups to be nothing more than metaphors expressing the sum of the attitudes held by their members. To say that students think tuition is too high is just a way of saying that most students think so. On the other hand, such attributions might be understood non-summatively as applying to collective entities, themselves ontologically distinct from the members upon which they depend. These so-called ‘plural subjects’ (Gilbert 1989, 1994, 2005) or ‘social integrates’ (Pettit 2003), while supervening upon the individuals comprising them, may well express attitudes that diverge from individual members. For instance, saying NASA believed the O-rings on the space shuttle’s booster rockets to be safe need not imply that most or all the members of this organizations personally held this belief only that the institution itself did. The non-summative understanding, then, considers collectives to be, like persons, apt targets for attributions of propositional attitudes, and potentially of moral and epistemic censure as well. Following this distinction, collective self-deception may be understood in either a summative or non-summative sense.