It's the time of year again. Tomorrow night, from 8:30 to 9:30 pm, no matter where you live in the world, it's Earth Hour.
By now, you probably know, the idea is turn off your lights for an hour to show your concern for the environment.
This year, organizers expect more than 7,000 cities and towns, across 152 countries and territories, on all seven continents to take part - including some newcomers.
The Palestinian territories, Rwanda, Tunisia, Galapagos, Suriname, French Guyana, and the remote island of St. Helena are all participating for the first time.
A number of major landmarks around the world will dim their lights during Earth Hour as well, including the CN Tower in Toronto.
Toronto was actually the second city to be part of Earth Hour.
And this week, Vancouver was named the winner of the Earth Hour city challenge for its "overall holistic and strategic approach to climate action".
It beat out 16 other finalists, including San Francisco, New Delhi, Oslo, and Sydney, Australia.
The campaign, led by the World Wildlife Fund, has grown immensely since it started - from 2.2 million participants in 2007 to an estimated 1.8 billion people last year.
Last month, at the global media launch for Earth Hour 2013, the CEO and co-founder Andy Ridley said...
"People from all walks of life, from all nations around the world, are the lifeblood of the Earth Hour interconnected global community."
"They have proven time and time again that if you believe in something strongly enough, you can achieve amazing things. These stories aren't unique, this is happening all over the world."
Here's the official video for this year's campaign, entitled "I Will If You Will".
Of course, there are critics who say Earth Hour is just symbolic and doesn't do anything tangible for the planet.
One of those critics is Bjorn Lomborg, an academic and environmental writer who wrote a best-selling book The Skeptical Environmentalist.
"Global warming is a real problem, but Earth Hour is not the answer," Lomborg told The Guardian.
"Taken to its logical conclusion, if switching the lights off for one hour is a good idea, why not for all the other 8,759 hours of the year?"
Below is a video from Lomborg and you can read a piece he did for Slate.com here.
Some energy experts also say that when everyone turns their lights back on, it puts a big strain on the power grid - contradicting the point of Earth Hour
But Ridley and the WWF say the campaign is about raising awareness for the long term, not saving energy for an hour.
"People from all walks of life, from all corners of the globe have been empowered to do what they can - both individually and collectively - to secure a sustainable future for the planet," Ridley told the International Business Times.
You can go to the WWF Canada's Earth Hour web page and pledge to save energy and change your habits long after tomorrow's event is done.
The idea is to spread the word through social media and get your family, friends, and colleagues to sign up too.
Other key landmarks that are marking Earth Hour include the Sydney opera house and Harbour bridge, the Great Wall of China, the Eiffel Tower, the Empire State building & Times Square, the British Houses of Parliament & Buckingham palace, Niagara Falls, the Las Vegas strip and more including...
The Brandenburg Gate in Berlin
Petronas towers in Kuala Lumpur, Malaysia
Marina Bay Sands in Singapore
The Bird's Nest in Beijing
The Gateway of India in Mumbai
The world's tallest building the Burj Khalifa, United Arab Emirates
The Ancient Citadel of Erbil in Kurdistan
Table Mountain in Cape Town, South Africa
The Bosphorus Bridge in Istabul, Turkey
The Walls of Dubrovnik in Croatia
The Little Mermaid statue in Copenhagen, Denmark and the Statue of David in Florence, Italy are among the landmarks turning off lights for the first time.