11 Downing Street (commonly known as Number 11), is the official residence of the Second Lord of the Treasury, who in modern times has always been the British Chancellor of the Exchequer.

The address is adjacent to the more famous 10 Downing Street, official residence of the First Lord of the Treasury, who since the early years of the 20th century has always been the Prime Minister of the United Kingdom. Many internal refurbishments over the years have obscured the buildings to the point that they can appear to be one single complex.