The harm principle is a central tenet of the political philosophy known as liberalism, and was first proposed by English philosopher John Stuart Mill. The principle states that people should be free to act however they wish unless their actions cause harm to somebody else. The harm principle is not designed to guide the actions of individuals but to restrict the scope of criminal law and government restrictions of personal liberty. According to Mill, the only purpose for which power can be rightfully exercised over any member of a civilized community against his will is to prevent harm to others. Importantly, Mill believed the harm principle only applied to people who are able to exercise their freedom responsibly. For instance, paternalism over children was acceptable since children are not fully capable of responsibly exercising freedom, but paternalism over fully autonomous adults was not.

Critics of the harm principle argue that it is too vague or broad to be useful and does not adequately define harm. Scholars have also argued that the harm principle does not provide a narrow scope of which actions count as harmful towards oneself or the population and it cannot be used to determine whether people can be punished for their actions by the state. A state can determine whether an action is punishable by determining what harm the action causes. If a morally unjust action occurs but leaves no indisputable form of harm, there is no justification for the state to act and punish the perpetrators for their actions.

In contemporary India, the harm principle means that the freedom of an individual can rightfully be restricted only to prevent harm to others.