2017 marks the tenth Earth Hour celebration and millions of people from around the world will switch off their lights to show their support for climate change.
The global event - which was created by World Wide Fund for Nature (known as WWF) - is the world's biggest environmental occasion.
If you want to take part and learn more about it, here's everything you need to know.
What is Earth hour?
The first ever event was held in Sydney in 2007 when 2.2 million people and more than 2,000 businesses turned their lights off for one hour to take a stand against climate change.
The following year Britain joined and the event has been growing in popularity ever since.
In 2013 local communities and businesses in Uganda created the first Earth Hour forest. It was built to fight against the 6,000 hectares of deforestation that occurs in the country every month.
When is Earth Hour?
It will take place this weekend on Saturday 25 March at 8:30pm. Millions of people around the world are expected to switch off their lights for one hour.
Participants from more than 170 countries will be taking part.
Why do people turn off lights?
It isn't about showing how much energy you can save by turning off your lights. It is more about highlighting the environmental issues facing the planet.
Which landmarks will switch off?
Iconic landmarks - such as Buckingham Palace, the Gherkin, the London Eye, Big Ben, Harrods, Olympia London, the BT Tower, the OXO Tower, Canary Wharf (One Canada Square) Brighton Pier and Edinburgh Castle - will be plunged into darkness.
The stadiums of football teams like Liverpool, Arsenal and Queens Park Rangers will also be switching off.
Elsewhere in the world New York's Empire State Building, the Eiffel Tower in Paris, the Sydney Opera House and Shanghai's iconic skyline will also join in.
How can I get involved?
Taking part doesn't necessarily mean you have to sit in the dark for an hour. How about organising a candlelit dinner with your friends?
You could also read a book with a torchlight, go stargazing or host an Earth Hour party.
Why not try having a candle-lit workout session with your friends? Yoga would be a great exercise for this.
There will also be local events hosted in your area - visit the WWF website to find out what's going on near you.
How can I donate?Supporters can share their commitment to the planet by donating five Facebook posts on their time line to Earth Hour on Change Climate Change website.
Alternatively, you can donate via the Earth Hour website.