The Royal Albert Hall, OXO Tower and Leadenhall Building are among the London landmarks that will plunge themselves into darkness on 19 March.
It's part of an hour-long lights-off initiative to support the World Wildlife Fund's Earth Hour campaign.
During the annual event, organisations and individual people are encouraged to turn the lights off to raise awareness of environmental issues.
Last year 10.4 million people in 172 countries and territories joined in, with landmarks including the BT Tower and Tower Bridge joining in.
Find out which landmarks, businesses and organisations are taking part this year, and sign yourself up here.
Afraid of the dark? Not to worry — it's only non-essential lights that get switched off — and in a city as busy as London, that means that many street lights remain on.
Earth Hour is on 19 March at 8.30pm — or make like this lot and get out and about taking some unique photos of London with the lights out.