Britain's new proposals to break the Brexit deadlock largely focus on arrangements for the border between the Irish republic and Northern Ireland after the country leaves the EU.
The issue of how to respect the EU's rules while adhering to the Good Friday Agreement has been a key sticking point in talks.
Here are the main points of the 1998 peace deal, which brought an end to decades of sectarian conflict that left thousands dead in the British-run province.
- Declaration of support -
The landmark agreement, also called the Belfast Agreement, was signed on April 10, 1998 between the then-prime ministers of Britain and Ireland, Tony Blair and Bertie Ahern.
Eight political parties or groupings also signed the document, stating in the text it was a "truly historic opportunity for a new beginning".
Three decades of violence between mostly Catholic republicans on one side and mainly Protestants unionists on the other had left a "deep and profoundly regrettable legacy of suffering".
"We must never forget those who have died or been injured, and their families," they wrote.
"But we can best honour them through a fresh start, in which we firmly dedicate ourselves to the achievement of reconciliation, tolerance, and mutual trust, and to the protection and vindication of the human rights of all."
The declaration committed participants to "partnership, equality and mutual respect as the basis of relationships" and "exclusively democratic and peaceful means".
- The border -
The agreement has little specific to say about border arrangements, and the word is only mentioned 10 times in the entire text.
The most explicit commitment by Britain and Ireland is to develop "normalisation of security arrangements and practices", including the "removal of security installations" and "other measures appropriate to and compatible with a normal peaceful society".
In effect, that has created an invisible border between north and south, satisfying republicans who wanted a united Ireland, and unionists who wished Northern Ireland to stay British.
That was helped by both Ireland and the UK being in the EU, but with Britain out, it would be more problematic -- both practically and, as many have pointed out, psychologically.
Irish prime minister Leo Varadkar has said the existing arrangement needed to stay and any return to a hard border would violate those Good Friday Agreement obligations.
Residents living on both sides of the border say any physical infrastructure on the frontier would reintroduce an actual divide -- and potentially fuel fresh violence.
- Disarming -
Signatories reaffirmed their commitment to the total disarmament of all paramilitary organisations.
They also confirmed their intention to achieve the decommissioning of all paramilitary arms within two years.
A new human rights commission and equality commission was charged with ensuring respect for religious and cultural preference.
- Constitutional issues -
The negotiators recognised "the legitimacy of whatever choice is freely exercised by a majority of the people of Northern Ireland", including their freedom to choose union with Britain or Ireland.
In addition, they recognised that a majority favoured British rule and declared that Northern Ireland would remain part of Britain.
If this majority wish were to change, as indicated in a referendum, London agreed to enact legislation to allow Northern Ireland to become part of Ireland.
For this purpose, London and Ireland both revoked their constitutional claim to sole sovereignty over Northern Ireland.
- Democratic institutions -
The agreement provided for an elected 108-member assembly in Belfast, with responsibility for finance, economic development, health, education, welfare, environment and agriculture. Other responsibilities would remain with London.
The assembly would be led by a first minister and deputy first minister with a power-sharing balance between unionists and nationalists.
The agreement also set up a North/South Ministerial Council, bringing together assembly members and their counterparts in Dublin on issues of "mutual interest".