The UK as a whole pays in more to the EU budget than it gets back.
But research by Cardiff University shows that Wales is a net recipient of EU funds, as more EU money comes to Wales, than it effectively pays into the EU through the UK's contribution.
How do the figures break down?
According to the Cardiff University research, in 2014 Wales received £396m from European structural funds, which was invested in roads, museums, universities and other big projects.
It also received £260m from the Common Agricultural Policy, to support farmers.
Another £2m from other programmes bring the EU total to Wales in 2014 to £658m.
On the other hand, Wales contributes to the EU budget through taxation.
The Cardiff researchers calculated that was worth £414m, bringing Wales' net receipts from the EU to £245m.
Both the UK contribution to the EU budget and the funds the EU transfers to the UK vary from year to year.
Wales' receipts from the EU would therefore be slightly different in 2015, but the 2014 Cardiff University figure is a good indication of the amounts Wales receives.
Is Plaid talking about its total or net receipts from the EU?
Plaid says it would demand that the full amount of EU funding is replaced by Westminster, not the net figure.
The party says that's £680m a year, slightly higher than the 2014 figure calculated by Cardiff University.
Will Westminster pick up the tab?
During the referendum campaign,  Leave campaigners, including the current Foreign Secretary, Boris Johnson, said all programmes in Wales would be funded at current levels until 2020, "or up to the date when the EU is due to conclude individual programmes".
But after the EU referendum, Welsh Secretary Alun Cairns announced in the House of Commons that "simply replacing what are currently EU funds with another source from Westminster misses the point".
The UK government has not laid out its funding plans for Wales after the UK leaves the EU.
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Plaid Cymru released its general election 2017 manifesto on 16 May and pledged to demand from the government in Westminster "every single penny" of the money Wales currently receives from the EU, once the UK leaves the bloc.