Reality Check: How many people are affected by May's offer?
Theresa May told other EU leaders on Thursday that a new "UK settled status" would grant EU migrants who had lived in the UK for five years, rights to stay and access to health, education and other benefits.
She said the proposals depend on other EU states guaranteeing UK citizens the same rights.
So, how many EU nationals live in the UK and where do they come from? And which of the other 27 EU countries host most UK citizens?
The number of citizens of the other 27 EU countries living in the UK in 2015 was estimated by the Office of National Statistics (ONS) to be around 3.2 million.
Polish citizens topped the list with 916,000 - more than any other nationality. In 2001, there were only 38,000 Polish nationals living in the UK.
Irish nationals are the second largest EU group in the UK, estimated at 332,000 in 2015.
In 2001, there were only 5,000 Romanians living in the UK. Romania joined the EU in 2007, but its citizens were not allowed to seek employment in the UK freely until 2014. There are now 233,000 Romanians living in the UK, making them the third biggest EU group of migrants.
There has been a notable increase in the number of migrants from the older EU member states too: Italy, France, Germany, Spain and Portugal.
An analysis by the ONS, published in January 2017, suggests that an estimated 900,000 UK citizens are long-term residents of other EU countries.
Spain hosted the highest number of migrants from the UK with 309,000. More than 100,000 of them are aged 65 and over. France was second with 157,062, and Ireland third with 112,090.
These numbers are all estimates, generally based on extrapolations of countries' censuses, which are carried out every 10 years.