 Virtually every aspect of self-deception, including its definition and paradigmatic cases, is a matter of controversy among philosophers. Minimally, self-deception involves a person who seems to acquire and maintain some false belief in the teeth of evidence to the contrary as a consequence of some motivation, and who may display behavior suggesting some awareness of the truth. Beyond this, philosophers divide over whether self-deception is intentional, involves belief or some other sub-or-non-doxastic attitude, whether self-deceivers are morally responsible for their self-deception, and whether self-deception is morally problematic (and if it is in what ways and under what circumstances), whether self-deception is beneficial or harmful, whether and in what sense collectives can be self-deceived, how this might affect individuals within such collectives, whether our penchant for self-deception was selected for or merely an accidental byproduct of our evolutionary history, and if it was selected, why?