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An interior ministry (sometimes ministry of internal affairs or ministry of home affairs) is a government ministry typically responsible for policing, emergency management, national security, registration, supervision of local governments, conduct of elections, public administration and immigration matters. The ministry is often headed by a minister of the interior, minister of internal affairs or a 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 some countries, policing and national security belong to a separate ministry (often titled "ministry of public order", "ministry of security" etc.), with the interior ministry being limited to control over local governments, public administration, elections etc. Notable examples include Greece ( ministry of citizen protection) and Israel ( ministry of public security).
In countries with a federal constitution, an interior minister will often be found at both the federal and sub-national 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 natural resources, 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 functions such as public safety and disaster relief), with some others falling under the Department of Justice (with functions such as handling the national police and the management of prisons).
In Canada the Interior Minister's post existed from 1873 to 1936, replacing previous role of the Secretary of State for the Provinces. The current position is held by the newer Minister of Public Safety since 2003.
In Hong Kong, the Secretary for Home Affairs is responsible for matters relating to communities, culture, sports and local governance. Policing and related matters are the responsibilities of the Secretary for Security.
In India, the Ministry of Home Affairs (MHA) is responsible for internal security, demographics, promotes the official language.  It tasks specialized functions by virtue of its departments, namely Department of Border Management, Department of Internal Security, Department of Jammu & Kashmir Affairs, Department of Home, Department of Official Language and Department of States. As such it heads such functions as the internal intelligence, and police and Civil Services of India as also protocol, freedom fighter pensions and manning of the courts. 
In Japan, law enforcement is decentralised with the National Public Safety Commission coordinating between the National Police Agency and the government through its chairman, who is a cabinet member. National security and immigration matters fall under the Ministry of Justice, whilst the Ministry of Internal Affairs and Communications handles the administrative system, local government, elections, telecommunication and post matters.