There are lots of reasons why people from overseas come to live here but not everyone agrees whether they should or not.
On Monday, the government made plans to control the numbers arriving both legally and illegally.
Who lives in the UK?
The UK is made up of people from loads of different countries. Some have been here for years, others for only months or even days.
Why do they come here?
Most immigrants come here looking for a better life. Many want somewhere safe away from war or because they think Britain has more to offer - with education, work and healthcare.
So what's the problem?
Not everyone agrees that Britain should be home to so many people. Some think that there just aren't enough jobs or money to go round. But others believe that we're lucky to have a developed and trouble free country and so we should open our doors to them.
What will the Government do?
The Government now wants to control the numbers of immigrants coming into Britain and plan to make changes over the next five years.
They want to encourage immigrants into the UK only if they have the skills the country needs.
They'll tighten borders and make checks on air routes used by illegal immigrants.
And those who aren't successful with their application to stay will be sent back home.
Immigration looks likely to be a big issue at the next general election, rumoured to be in May.