Makeshift camps in the French port town of Calais are being demolished by the French authorities.
It's thought there are between 3,500 and 6,000 people living in tents and shelters there but nobody really knows.
Between 800 and 3,500 refugees are affected, with officials trying to force them to move into converted containers to live.
Riot police have been firing tear gas at migrants who have been hurling stones at the demolition teams.
More trouble has broken out between migrants and police.
They want to stay in the camp - known as The Jungle - but the French authorities want to reduce the size of the camp and move refugees into shipping containers.
Officials are calling it a "humanitarian operation".
But the story begins a long way from Calais.
Refugees travel from as far as Syria, Iraq, Sudan and Eritrea.
These are countries where civil wars rage or where human rights are poor.
They risk their lives crossing the sea and smuggling themselves into Europe.
They walk across Europe to reach countries they want to settle in. There have been various camps around Calais since 2002 but more and more people have arrived in recent years.
There are hundreds of unaccompanied children.
Some charities say there are more than 400 children living in the camp without any parents.
There's concern for their safety and their mental health.
Life in the camp is cold, dirty, miserable and hard.
Some sleep on the floor covered with a few thin sheets of cardboard.
The temperatures often go below zero and plastic bags are used to keep the cold draft from blowing through holes in tents.
Many people living in the Calais Jungle want to reach the UK.
Each day groups of migrants walk to the Channel Tunnel terminal, hoping to hide on trucks heading to Britain.
French police say there are too many migrants to arrest or deal with properly. Some are just freed and then try again to reach the UK.
Many migrants fear they will be required to claim asylum in France if they move into the shipping containers, meaning they'll have to give up hope of travelling to Britain to live.
At least 18 people have died since last June trying to get across the Channel.
And people have started to try and help smuggle children into the UK.
The UK says it will take 20,000 Syrian refugees by 2020.
But some say that's not enough.