In Zadig, published in 1748, Voltaire wrote of “the great principle that it is better to run the risk of sparing the guilty than to condemn the innocent.” At about the same time, Blackstone noted approvingly that “the law holds that it is better that ten guilty persons escape, than that one innocent suffer.” In 1824, Thomas Fielding cited the principle as an Italian proverb and a maxim of English law. John Stuart Mill endorsed it in an address to Parliament in 1868. General acceptance of this maxim continues into our own period, yet it is difficult (and for us so far, impossible) to find systematic attempts to defend the maxim. It is treated as a truism in no need of defense. But the principle within it is not at all obvious; and since it undergirds many of our criminal justice policies, we should be sure that it is justifiable. First, however, we must clarify what the principle means.