An interior ministry (sometimes ministry of home affairs) is a government ministry typically responsible for policing, national security, and immigration matters. The ministry is often headed by a minister of the interior or minister of home affairs. In some countries, matters relating to the maintenance of law and order and the administration of justice are the responsibility of a separate justice ministry.

In countries with a federal constitution, an interior minister will often be found at both the federal and state levels. Similarly, autonomous entities and dependent territories may also have interior ministers.

In certain jurisdictions, similarly named government departments may have other responsibilities. In the United States, the Department of the Interior has radically different functions—primarily the management and conservation of land owned by the federal government, and programs and policies dealing with indigenous peoples of the U.S. The functions that fall under what most other countries call an "interior ministry" are under other government departments—mostly the Department of Homeland Security, with some others falling under the Department of Justice.