Smith Square is a square in Westminster, London, 250 metres south-southwest of the Palace of Westminster. Most of its garden interior is filled by St John's, Smith Square, a Baroque surplus church, the inside of which has been converted to a concert hall. Most adjoining buildings are offices, with the focus on organisations lobbying or serving the government. In the mid-20th century, the square hosted the headquarters of the two largest parties of British politics, and it is now hosts much of the Department for Environment, Food and Rural Affairs and the Local Government Association. It has a pedestrian or mixed approach to the four sides and another approach to the north.

St John's Smith Square is a redundant church in the centre of Smith Square, Westminster, London. Sold to a charitable trust as a ruin following firebombing in the Second World War, it was restored as a concert hall.