Queen Elizabeth arrived at Hillsborough Castle, Co Down, last night for the start of a three-day visit to the North to mark her golden jubilee.
Her engagements will include addressing members of the Northern Ireland Assembly at Stormont.
She will also attend a service at St Anne's Cathedral at which the leaders of the four main churches will be present.
Police are mounting a major security operation for the visit. Security sources have expressed concern about the dissident republican threat.
The Ulster Unionist Party president, the Rev Martin Smyth, called on loyalists and republicans to show respect to the queen by not marring her visit with violence.
The queen is accompanied by her husband, the Duke of Edinburgh. She will attend garden parties in Cookstown and Hillsborough.
The SDLP is expected to be represented at all the relevant functions, reflecting the party's role in the Northern Ireland administration. Sinn Féin will not be present.Queen Elizabeth will return to England tomorrow afternoon.
It is her 15th visit to the North. Her last was in November 2001 when she visited Derry, Banbridge and Lisburn.
During her silver jubilee visit in 1977, there was a major security alert at the University of Ulster in Coleraine, Co Derry. A bomb was later discovered on the campus.
Every police officer is expected to be on duty during the current visit.
Around 1,200 people will attend a garden party today at Loughry College in Cookstown, Co Tyrone, and there will be 3,000 guests at a similar event in Hillsborough Castle tomorrow.
Mr Smyth said the North would be under the spotlight during the visit.
"It should not be marred for the rest of the community by a minority of individuals, republican and loyalist," he said.
The recent sectarian violence in Belfast was inexcusable at any time and should end immediately, he added.
"Anyone engaged in such activities over the next few days will be delivering a sign of disrespect to the queen and should hang their heads in shame."
Republican Sinn Féin has voiced opposition to the visit. "She is chief of her murderous army of occupation just as war criminals Bush and Sharon are chiefs of their armies," a party leaflet distributed in nationalist areas says.