Some migrants sent back from Greece to Turkey
4 April 2016 Last updated at 16:38 BST
More than a million migrants and refugees have come to Europe in the last year, to try and start a new life.
People coming from countries like Syria, Iraq and parts of Africa often travel by boat from Turkey to get to other European countries.
One of the places that they get to first is Greece, which has been overwhelmed by the large number of people who have arrived there.
BBC reporter Sarah Rainsford sent us this report from Greece, where some migrants are leaving by boat to go to Turkey as part of the new plan - she explains what's happening there.