This essay, for a symposium on Citizen Ignorance, Police Deception and the Constitution, relies on moral philosophy and new empirical research in arguing that police deceit during interrogation is permissible when: (1) it takes place in the window between arrest and formal charging; (2) it is necessary (i.e., non-deceptive techniques have failed); (3) it is not coercive (i.e., avoids undermining the rights to silence and counsel and would not be considered impermissibly coercive if true); and (4) it does not take advantage of vulnerable populations (i.e., suspects who are young, have mental retardation, or have been subjected to prolonged interrogation). A prohibition on interrogation deception under these conditions would cause much more harm (in terms of lost true confessions) than benefit (in terms of preventing false confessions and any intangible harm to the dupe or society).