The DUP was founded in 1971 by the Reverend Ian Paisley and William Boal, an MP who defected from the Official Unionists in protest at the policies of the then Prime Minister of Northern Ireland, Terence O'Neill.
The DUP led opposition to the Sunningdale power-sharing executive in 1974.
Under Rev Paisley's leadership it has strongly opposed the Good Friday
It is similarly against any other move which it interprets as an attempt to weaken the union or as a concession to nationalists or the Republic.
Although it has now taken up two ministerial posts on the executive, the DUP still refuses to have dealings with Sinn Fein members of the same body.
The DUP is also strongly anti-Catholic in the religious sense. Mr Paisley often denounces the Pope.
The party has two MPs at Westminster and 20 assembly seats.