Thousands of landmarks are to switch off their lights for an hour this month, while millions of people around world will stage fundraisers.
This year marks the tenth Earth Hour - the worlds biggest environmental event.
Hundreds of millions of people in countries and territories around the world will show they care about our planet by switching their lights off at 8.30pm for one hour.
Below we've pulled together all of the information about the event, so you can do your bit and join in by switching off your lights.
What is Earth Hour?
Earth Hour is the world's largest grassroots movement for the environment, organised by WWF.
The event first started Sydney in 2007, in an attempt to put climate change in the spotlight.
It is now celebrated across all continents, and has helped bridge the gap between the grassroots and the corridors of power, taking climate action from conference rooms to living rooms.
In Argentina, for example, Earth Hour has helped mobilise public support for the creation of a 3.4 million hectare-wide marine protected area, while in Uganda, local communities and businesses have created the first Earth Hour forest.
"We started Earth Hour in 2007 to show leaders that climate change was an issue people cared about," said Siddarth Das, Executive Director, Earth Hour Global.
"For that symbolic moment to turn into the global movement it is today, is really humbling and speaks volumes about the powerful role of people in issues that affect their lives."
When is Earth Hour?
Earth Hour 2017 will take place on Saturday 25 March at 8:30 pm local time, when millions of people in over 170 countries across the world will switch off their lights for one hour to show they care about the future of our planet.
Why do people turn the lights off?
Earth Hour is not about how much energy is saved during the hour, but about putting the spotlight on the issues facing the planet and inspiring people to live more sustainably.
The idea is that the choices people make and the actions they take after the hour is up can help reduce the impacts of climate change on the planet, its wildlife and future generations.
"Every flick of a switch is a reminder that people see themselves as an integral part of climate action," said Das.
"It is this kind of collective determination we need to tackle the most pressing environmental challenge our planet has ever faced."
Which landmarks are turning off their lights this year?
Thousands landmarks and monuments joined the switch off last year, including the Empire State Building, the Eiffel Tower in Paris, the Sydney Opera House and Shanghai's iconic skyline.
This year, dozens of famous UK locations have signed up to take part, including Buckingham Palace, the Gherkin, the London Eye, Big Ben, Harrods, Olympia London, the BT Tower, the OXO Tower and Canary Wharf (One Canada Square).
The stadiums of football teams such as Liverpool, Arsenal and Queens Park Rangers will also be plunged into darkness.
Other notable spots taking part around the country include Brighton Pier, Windsor Castle, Durham Cathedral, the Angel of the North and Liverpool's Radio City Tower.
A number of UNESCO World Heritage sites traditionally take part, including the Acropolis in Athens and Edinburgh Castle, and thousands of schools also do their bit by switching off.
How can you play a part?
WWF say it's completely up to individuals how they take part during the hour - just as long as the lights are out!
"It's not about sitting in the dark for an hour," WWF says.
"Whether someone is enjoying their favourite book, getting together with friends for a candlelit (dinner) party or stargazing with loved ones, it's their event too."
WWF has put together a list of 60 things you can do in the dark for those in need of a bit of inspiration.
If you're taking part in Earth Hour, you can add your name to the official website to tell the world, and view on the map what other people are doing.
How can you donate?
As skylines darken, people will be invited to take a stand for climate action on their Facebook timelines through the Donate Your Feed platform.
Supporters can also share their commitment to the planet by donating five Facebook posts on their timeline to Earth Hour on www.earthhour.org/climateaction .
Alternatively, you could set up your own JustGiving fundraising page and encourage people to donate, or donate via the website earthhour.wwf.org.uk/fundraising/ .