The first woman ever to be British Prime Minister, Margaret Thatcher, has died peacefully aged 87.
She was in charge of the country for 11 years as leader of the Conservative party between 1979 and 1990 and had a huge influence on Britain.
A statement released by her family said: "It is with great sadness that Mark and Carol Thatcher announced that their mother Baroness Thatcher died peacefully following a stroke this morning."
The union jack flags above the Houses of Parliament and Number 10 Downing Street have been lowered to half-mast as a mark of respect.
David Cameron called her a "great Briton" and the Queen has spoken of her sadness at hearing of the death; while Barack Obama said "America has lost a true friend".
Baroness Thatcher's funeral will be of a similar status to those of the Queen Mother and Princess Diana.
The ceremony, with full military honours, will take place at London's St Paul's Cathedral.
An influential figure
From the start of her time as prime minister she divided opinion. When she came to power in 1979 she wanted to make big changes to how the country was run.
One of her biggest changes was that she wanted private companies and people, and not officials, to run government-owned things like British Gas and BT (British Telecom). She believed that private companies would run the services better.
Margaret Thatcher was thought to have survived on just four hours sleep a night - and got the nickname "the Iron Lady" for being tough and sticking to her decisions.
After 11 years in power - and winning three elections - she'd been prime minister for longer than anyone else in the 20th century.
But eventually even her own party thought she had been in charge too long - and she left Downing Street in tears.
Now, more than 20 years on, she is recognised as a prime minister who transformed the face of Britain - and will be remembered as one of the most important figures in modern British history.