This paper advocates for a general policy of penal leniency: judges should often sentence offenders to a punishment less severe than initially preferred. The argument’s keystone is the relatively uncontroversial Minimal Invasion Principle (MIP). MIP says that when more than one course of action satisfies a state’s legitimate aim, only the least invasive is permissibly pursued. I contend that MIP applies in two common sentencing situations. In the first, all sentences within a statutorily specified range are equally proportionate. Here MIP (...) applies directly. In the second, judges reasonably believe that one of the sentences within the range is the most proportionate, but can’t identify it with any certainty. In these cases of sentencing uncertainty, judges must be indifferent between their preferred sentence and a softer one, and this indifference triggers MIP. MIP thus frequently mandates some degree of leniency. I conclude with some comments on statistical uncertainty. (shrink)