A cathedral service, a minute's silence and community sing-along will mark the first anniversary of the Manchester Arena attack.
Twenty-two people were killed and hundreds injured when a bomb was detonated at the end of an Ariana Grande concert on 22 May 2017.
Who will be at the memorial service?
Hundreds of those injured in the explosion, and the families of those killed, will be attending a remembrance service at Manchester Cathedral.
The Duke of Cambridge and Mrs May will join the families, as well as emergency workers who went to their aid.
Only those with invitations can attend, but people will be able to watch the service on a big screen in the nearby cathedral gardens, and further afield at York Minster, Liverpool Metropolitan Cathedral and Glasgow Cathedral.
Greater Manchester Mayor Andy Burnham said it was a day to "come together", tweeting: "Today ... we remember each of the 22 people whose lives were taken & we re-commit to supporting their families & all affected."
The service will incorporate a national silence at 14:30 BST, which will also be marked at UK government buildings.
Capturing city's spirit in song
The Manchester Together With One Voice event takes place between 19:00 BST and 21:00 BST and will bring together choirs from the city and beyond.
Among those performing are the Manchester Survivors Choir, a group made up of people who were at the arena on the night of the concert.
The final half hour will be a sing-along, broadcast live on BBC Radio Manchester, featuring songs including Grande's One Last Time, One Day Like This by Elbow, Don't Look Back In Anger by Oasis and Never Forget by Take That.
Families of the 22 people killed were invited to select lyrics, and members of the public were asked to make suggestions online.
Manchester City Council leader Sir Richard Leese said music was "in Manchester's soul", as was shown in the aftermath of the attack when "spontaneous song captured the city's spirit".
A crowd sang a rendition of Don't Look Back In Anger by Oasis in the days following the attack.
He said: "Coming together in song will once again demonstrate that remarkable sense of togetherness."
Bells will toll in tribute
At 22:31 bells across the city centre will ring out to mark the moment of the explosion.
Bells at Manchester Town Hall, St Ann's Church and St Mary's Roman Catholic Church will sound in tribute to the victims.
Shining a light on city square
A further event, named There Is A Light, will run between Tuesday and Saturday with song lyrics projected on to St Ann's Church and other parts of St Ann's Square.
St Ann's Square became a focal point for tributes in the wake of the bombing, with many thousands of wreaths left by well-wishers.
Some of the flowers were later composted and the soil used for the Trees of Hope trail, where trees were planted around the city centre.
Members of the public can write messages on special tags to be attached to the Japanese maple trees until Tuesday evening.
How can people watch the events?
13:45 BST to 15:15 BST: Special coverage of the National Service of Commemoration, on the first anniversary of the Manchester Arena attack, including a minute's silence at 14:30 BST.
19:00 BST to 21:00 BST: Special coverage of the "Manchester Together" commemoration event.