This chapter discusses the nature of the harm principle and its implications for toleration of individuals and their behavior. Defending a principled basis for the limits of toleration is intended to have practical, action-guiding value—primarily for polities, but also more generally. The chapter attempts to both demonstrate and improve on that by showing where the limits are in different arenas. It begins by looking at ideas for understanding different variations of the harm principle, particularly by David Brink and James Edwards, to help better explicate the own take on the principle. The chapter looks at the implications of this principle for individuals within a single polity, including looking to see what sort of interferences might be permissible when there is harm. It argues that the liberal state should tolerate autonomous sacrifices of autonomy, including instances where an individual chooses to become a slave, to be lobotomized, or to be killed.