The title Lord-Lieutenant is given to the British monarch's personal representatives around the United Kingdom. Usually some retired local notable, a senior army officer, peer or business person is given the honorary post.

Lord-Lieutenants are the monarch's representatives in their lieutenancy. It is their foremost duty to uphold the dignity of the Crown, and in so doing they seeks to promote a spirit of co-operation and good atmosphere by the time they give to voluntary and benevolent organisations and by the interest they take in the business and social life of their counties.

The modern responsibilities of Lord-Lieutenants include:

• Arranging visits of members of the Royal family and escorting Royal visitors;
• Presentation of medals and awards on behalf of the Sovereign, and advising on Honours nominations;
• Participation in civic, voluntary and social activities with the Lieutenancy;
• Liaison with local units of the Royal Navy, Royal Marines, Army, Royal Air Force and their associated cadet forces;
• Leading the local magistracy as Chairman of the Advisory Committee on Justices of the Peace; and
• Chairing the local Advisory Committee for the Appointment of the General Commissioners of Income Tax, a tribunal which hears appeals against decisions made by the Inland Revenue on a variety of different tax related matters.

Originally a Lord-Lieutenant was assigned to each of the traditional counties, but these boundaries have not matched for hundreds of years. In England and Wales the areas they are assigned to are known as ceremonial counties. In Scotland the phrase used is simply lieutenancy areas.

The City of London is a special exception as it has a Commission of Lieutenancy rather than a single Lord Lieutenant. The Head of the Commission is the Lord Mayor of London.

In Northern Ireland there are eight Lieutenants, for each of the six traditional counties of Antrim, Armagh, Down, Fermanagh, Londonderry and Tyrone and for the county boroughs of Belfast and Londonderry.

See: Ceremonial counties of England, Lieutenancy areas of Scotland, Ceremonial counties of Wales; Lists of Lord Lieutenants.

The Lord Lieutenant of Ireland was the head of the British administration in Ireland until the foundation of the Irish Free State in 1922.