Hundreds of experts from around the world have travelled to Indonesia for a big meeting aimed at saving our planet for future generations.
They are focussing on climate change. We're always hearing about how we can do things to stop our world heating up.
But whole countries need to change their behaviour to have a real impact, the experts say.
Top of the list of things to do is to stop pumping so many harmful gases - like carbon dioxide - into the air.
They also want people to stop cutting down the trees that absorb the gases and to get everyone to agree to do more to protect the world.
One place that's really under threat is the island of Borneo in Malaysia. Its massive rainforests are sometimes called the lungs of the world.
The trees breathe in gases like carbon dioxide - which are harmful to us - and breathe out oxygen, cleaning the air for us.
But huge parts of the forests are being cut down every year and, with fewer trees to absorb the gases, we could be in a lot of trouble.
Experts are thinking about paying countries like Malaysia not to chop down their trees.
The effects of climate change have already been seen in some places.
Penguins under threat
In Antarctica, it's warmer than it used to be - meaning that some of the ice is melting.
Animal charities are concerned that if it keeps getting hotter, penguins could die out.
The challenge for those meeting in Indonesia this week is how to sort it out - before it's too late.