- Video report by ITV News Correspondent John Ray
Who gets to stay; who gets shown the door?
It’s a big and important question.
After all, the widely held desire to see migration reduced fuelled the Brexit vote.
So three years on, it might seem odd that the issue hasn’t merited much of a mention in this election.
Meanwhile, the main parties' manifestos are long on slogans and short on detail.
Or perhaps, given the toxic nature of the debate and the tough decisions to be made, that lack of precision isn’t a surprise at all.
The Conservatives promise to cut numbers - and Boris Johnson said on the last weekend of campaigning that EU citizens had treated "the UK as if it were part of their own country" for too long - but they’ve abandoned all those targets they used to miss with such embarrassing regularity.
Nor is there much meat on the bones of their "Australian-style points system" other than it will favour English speakers and those with a job to come to.
With an eye on its Brexit-voting supporters, Labour has shied away from its own conference demand to extend freedom of movement.
Instead it promises an immigration system based on the needs of the economy.
How that might work post Brexit isn’t clear.
The Liberal Democrats offer most clarity.
They would cancel Brexit and keep freedom of EU movement.
They’d also make it easier for asylum seekers to work.
So too for those who arrive as students and want to find a job after they graduate.
In their own ways, all the contenders are trying to square a circle.
And it’s best summed up by farmer Guy Poskitt in Yorkshire, whose carrot processing factory is almost entirely reliant on migrant labour.
"Nothing would please me more than to employ local people," he tells me.
"But migrant workers will support the needs of my business.
"Pack on Saturdays or on Boxing Day.
"Could I find a hundred local people to pack my carrots then?
"No chance," he adds.
In other words, if we send all those migrants packing, who’s going to fill all those boxes of carrots?
Or fill all those vacancies on our building sites, hotels, restaurants, research labs, and most notably, in the NHS; one in eight NHS workers comes from overseas.
We found one former GP who’s quit Britain for Malaysia.
Visa fees plus the surcharge for using the very services she works for drove Dr Siti Ibrahim to leave.
"Every doctor and healthcare professional is paying national insurance and tax," she told us.
Ms Ibrahim added: "Why are we having to pay the surcharge for something we are helping to run?"
Immigration on the scale Britain has witnessed over the past decade might not be popular, but as a nation we’ve become reliant on a supply of foreign labour - skilled, unskilled and all points between.
Who counts as an essential worker and who's deemed an unwanted arrival, it isn’t going to be easy to decide.