Margaret Thatcher holds her controversial Sermon on the Mound before the General Assembly of the Church of Scotland.

Margaret Hilda Thatcher, Baroness Thatcher, was a British stateswoman who served as Prime Minister of the United Kingdom from 1979 to 1990 and Leader of the Conservative Party from 1975 to 1990. She was the longest-serving British prime minister of the 20th century and the first woman to hold the position. As prime minister, she implemented policies that came to be known as Thatcherism. A Soviet journalist dubbed her the "Iron Lady", a nickname that became associated with her uncompromising politics and leadership style.

"Sermon on the Mound" is the name given by the Scottish press to an address made by British prime minister Margaret Thatcher to the General Assembly of the Church of Scotland on Saturday, 21 May 1988. This speech, which laid out the relationship between her religious and political thinking, proved highly controversial.

The General Assembly of the Church of Scotland is the sovereign and highest court of the Church of Scotland, and is thus the Church's governing body. It generally meets each year and is chaired by a Moderator elected at the start of the Assembly.

May 21 is the 141st day of the year in the Gregorian calendar; 224 days remain until the end of the year.