DUP-Tory deal: What is 'confidence and supply'?
THE deal between the Conservatives and DUP is expected to be a "confidence and supply" arrangement instead of a coalition.
It means the DUP would not formally be part of a Tory-led government and would not hold ministerial positions.
Instead, its MPs would agree to back Theresa May in votes of no confidence and major issues such as the budget, in return for support or funding for some of its own policies.
Confidence and supply deals tend to be loose and can leave governments constrained in what they can do, passing as little legislation as possible to avoid defeats.
They can also be unstable and short-lived, with the prospect of fresh elections being called if the deal between parties breaks down.
In the Republic, the Fine Gael-led minority government has since last year operated under a 'confidence and supply' agreement with rival party Fianna Fáil.
John Major started out with a Conservative majority in 1992 but was leading a minority government by the 1997 general election.
Labour's Harold Wilson and James Callaghan also governed with minorities for much of the 1970s.
In 1979, Callaghan's administration collapsed when he lost a crucial vote of confidence in the House of Commons.
Two unionist MP backed him in the crunch vote after striking a deal to get a gas pipeline to Northern Ireland.
But Callaghan still lost by one vote after former SDLP leader Gerry Fitt and independent republican Frank Maguire abstained.