Today's historic visit is a symbolic ending to the painful separation of British and Irish states, but 3000 unsolved murders remain.
Hyde Park bombing suspect John Downey will not face trial after being given false assurance he was not wanted over the 1982 IRA attack.
Fr Reid worked tirelessly for years to end the Troubles in Northern Ireland, today he died peacefully in hospital. He will be remembered.
In a speech today, Northern Ireland Secretary Theresa Villiers is expected to call for a focus on paramilitaries rather than the police as part of future measures to heal divisions over the conflict. She is expected to say:
At least with a new process, agreed by Northern Ireland's political leaders, there is scope to write in from the start the need for an objective balance and with proper weight and a proportionate focus on the wrongdoing of paramilitaries...rather than the almost exclusive concentration on the activities of the state which characterises so many of the processes currently under way.
The Northern Ireland Secretary is to call for "proportionate" focus on wrongdoing by republicans and loyalists rather than the police as part of future measures to heal divisions over the conflict.
Many processes for addressing the legacy of the past - during which thousands were killed or maimed amid 30 years of bombings and shootings - have concentrated on the activities of security forces, Theresa Villiers will argue, rather than paramilitaries who were responsible for most cases.
The devolved ministerial Executive at Stormont is spending more than £30 million a year on historical matters, with police trawling hundreds of thousands of documents, in part to investigate shootings carried out by former officers or soldiers.
A man has been arrested by police investigating the Omagh bomb. The Real IRA blast in 1998 killed 29 people and a woman pregnant with twins.
The suspect was detained in Newry, Co Down.
Martin McGuinness has described his decision to attend a banquet hosted by the Queen as "an important thing to do" that sends "a message to everybody about how things have changed".
Speaking today, the Northern Irish Deputy First Minister and former IRA commander said that "both governments, who have been rather sluggish over the course of recent times, would do well to learn the lessons of what is happening here in the course of next week".
"They have a huge responsibility to play and unfortunately they haven't been playing it in the last number of months," he added.
Mr McGuinness, who shook the Queen's hand in an historic first meeting in June 2012, said: "We're not just involved in a peace process - we're also involved in a change process.
He added that his acceptance was "an attempt by me to stretch out the hand of friendship" to the unionist and loyalist communities of Northern Ireland.
Irish Taoiseach Enda Kenny welcomed the decision to invite Northern Ireland deputy Prime Minister Martin McGuinness as a special guest of the Queen during the first official state visit of the President of Ireland to England.
The former MP, who refused to sit in the House of Commons because he would have had to swear an oath of allegiance to the Queen, previously did not attend a banquet in the Queen's honour at Dublin Castle in 2011.
Speaking on the BBC's Andrew Marr programmes, Mr Kenny said he did not see why the former IRA commander would not attend.
Mr Kenny also raised the prospect of a royal visit to Ireland during the centenary of the 1916 Easter Rising, when Ireland declared its independence and revolted against British rule.
The Queen met and shook hands with Martin McGuinness in Belfast two years ago, in what was a historic step forward in Anglo-Irish relations.
A Conservative MP has said he would feel "uncomfortable" sitting next to Northern Ireland Deputy First Minister Martin McGuinness, after it was announced that he would be a special guest of the Queen during a state banquet at Windsor Castle.
Andrew Rosindell said: "Whilst the man concerned has engaged in things in the past which have created appalling mayhem and tragedy, today we are looking at healing those rifts.
"I would feel very uncomfortable sitting beside him at dinner. I would have great difficulty doing that myself, but in terms of building a democratic foundation in Northern Ireland, I can understand why people feel this is what we need to do.
"But would I want to sit beside him at dinner? No, I certainly would not."
The Queen is "looking forward" to an historic state visit by Northern Ireland Deputy First Minister Martin McGuinness at Windsor Castle, Buckingham Palace has said.
A spokesman added: "There is a long-standing practice of not commenting in individual invitations. That said, Her Majesty is greatly looking forward to this historic state visit and welcoming all guests to Windsor Castle."
Sinn Fein President Gerry Adams has hailed a "new and positive relationship" between "all of Ireland and Britain" as it was announced that Martin McGuinness would attend an Irish state banquet hosted by the Queen.
"While Martin McGuinness's involvement in President Higgins's state visit may not be welcome by opponents of change, it is yet another example of Sinn Fein's commitment to an inclusive future based on tolerance and equality," he said.
He continued: "This decision may cause difficulty for some Irish republicans in light of ongoing difficulties in the north (of Ireland) but I would appeal to them to view this positively in the context of republican and democratic objectives and the interests of unity and peace on this island."
The banquet, in honour of Irish President Michael D Higgins, will be hosted at Windsor castle next week.
Northern Ireland's Deputy First Minister and ex-IRA commander Martin McGuinness will attend a state banquet at Windsor Castle in honour of the Irish president hosted by the Queen, it has been confirmed.