Malum in se (plural mala in se) is a Latin phrase meaning wrong or evil in itself. The phrase is used to refer to conduct assessed as sinful or inherently wrong by nature, independent of regulations governing the conduct. It is distinguished from malum prohibitum, which is wrong only because it is prohibited.

For example, most human beings believe that murder, rape, and theft are wrong, regardless of whether a law governs such conduct or where the conduct occurs, and is thus recognizably malum in se. In contrast, consider driving laws. In the U.S., people drive on the right-hand side of the road. In the UK and other states of the Commonwealth, people drive on the left-hand side. Violation of these rules is an example of a malum prohibitum law because the act is not inherently bad, but is forbidden by law, as set forth by the lawmakers of the jurisdiction. Malum prohibitum crimes are criminal not because they are inherently bad, but because the act is prohibited by the law of the state.

This concept was used to develop the various common law offences.