It's been one year since Greta first started her 'School Strike for Climate'.
She was 15 years old at the time and skipped school to protest outside the Swedish parliament, calling on world leaders to do more to help the environment.
She chose to miss classes every Friday and asked other young people around the world to do the same.
This evolved into a massive campaign movement called 'Fridays for Future'.
Over the last year it's grown, with millions of students in countries all over the planet inspired by Greta to take action and walk out of school.
And it's not just been a big year for her campaign, it's been a big year for her too.
Greta has made some high-profile speeches about the issues of climate change.
In March she became one of youngest people ever to have been nominated for a Nobel Peace Prize.
She also joined with the campaign group Extinction Rebellion in London, encouraging protesters to continue their fight to stop climate change.
In May she was named as one of the world's most influential people by Time magazine.
Afterwards, she posted on social media saying "Now I am speaking to the whole world".
In June the human rights group Amnesty International presented her with the 'Ambassador of Conscience' award for 2019.
In July Greta even made her music debut by recording an essay on climate change for The 1975's new album, as well as getting the first ever "Freedom Prize" from France's Normandy region for her role in the climate movement.
In August Greta set sail from Britain on a two-week boat journey to the US to take part in two climate change summits there.
She's also been named 'Game Changer Of The Year' at GQ Men Of The Year Awards 2019, appearing on the front cover of the magazine's October edition.
If she can achieve all that in one year, we can't wait to see what she does next!