Abstract: An evolutionary theory of self-deception-the active misrepresentation of reality to the conscious mind-suggests that there may be multiple sources of self-deception in our own species, with important interactions between them. Self-deception (along with internal conflict and fragmentation) may serve to improve deception of others; this may include denial of ongoing deception, self-inflation, ego-biased social theory, false narratives of intention, and a conscious mind that operates via denial and projection to create a self-serving world. Self-deception may also result from internal representations of the voices of significant others, including parents, and may come from internal genetic conflict, the most important for our species arising from differentially imprinted maternal and paternal genes. Selection also favors suppressing negative phenotypic traits. Finally, a positive form of self-deception may serve to orient the organism favorably toward the future. Self-deception can be analyzed in groups and is done so here with special attention to its costs.