The PSNI, backed up by the British army, is expected to mount a huge security operation in north Belfast this evening amid concerns that a return Orange Order parade past Ardoyne shopfronts could erupt into serious violence.
There are a number of contentious parades in today's Twelfth of July demonstrations but the main focus of concern is Ardoyne where a large nationalist protest against the Orangemen and their supporters is expected this evening.
There are also concerns around this morning's parade by the Ardoyne shops and also at Whiterock in west Belfast this morning where Orangemen will march on to the nationalist Springfield Road.
There is also potential for trouble to flare in other areas with thousands of Orange Order members and supporters and hundreds of bands participating in 18 parades throughout the North.
The largest parade is in Portadown which police hope will prove peaceful after Sunday's Drumcree parade and protest concluded without serious incident.
It is expected that the potentially difficult Orange parade in the nationalist west bank of Derry will be peaceful after Orangemen and nationalists reached an accommodation.
Tonight's return feeder parade involving, all told, about 400 Orangemen, bands and supporters past the Ardoyne shops is a major security concern.
Violence erupted there last year when nationalists, who were separated from the Orange marchers by huge security screens, fired missiles over the screens. In a second incident, British paratroopers who were isolated from their colleagues were attacked by nationalists.
Senior military personnel admitted that the soldiers were within only minutes of firing on the nationalists at the time. Leading republicans such as Gerry Kelly and Bobby Storey intervened to calm the situation.
This year, however, there is no guarantee that provisional republicans will act in a similar fashion. Sinn Féin politicians warned that because of the re-jailing of IRA Shankill bomber Seán Kelly, former IRA prisoners might not be inclined to maintain some form of restraint on nationalist protesters this evening.
How tonight unfolds could have wider political repercussions with some concerns that if trouble erupts it could delay the IRA issuing a statement on its future intentions. Currently there is an expectation that the IRA will respond to Sinn Féin president Gerry Adams's appeal to the organisation to fully embrace peace and democracy before the end of July. Trouble tonight could affect that predicted timing.
PSNI chief constable Sir Hugh Orde appealed for calm but insisted his officers are prepared for whatever eventuality arises. "I have more than enough resources to deal with anything I have to deal with," he said.
He urged community and political leaders to use their influence to try to ensure a peaceful Twelfth. "I don't think it's too late for any community leader to say 'Let's look at what needs to be done and how we can comply with the law'," he said.
"My officers and soldiers are in the middle of this. That's a very difficult place to be. We are more than capable of dealing with whatever happens. We will do our job, but other people have to do their job," added Sir Hugh.
Mr Adams also appealed for calm. He said the Parades Commission had "created an extremely dangerous situation in Ardoyne" and the Orange Order had been rewarded for refusing to talk with local residents. Its sole purpose, he said, was to cause offence. Sinn Féin had been working to ensure the situation did not "spiral out of control" and he appealed to young people "not to be provoked".