A memorial service is planned at Syracuse University in New York State, which saw 35 of its students killed.
The dead will also be remembered in a ceremony at the Lockerbie memorial in the Arlington National Cemetery in Washington DC.
Proceedings in the Dumfries and Galloway town have been designed to be "low key" in accordance with the wishes of the community.
"Places to remember" will be open throughout the day at Lockerbie Town Hall, Tundergarth Church and the Dryfesdale Lodge Visitors Centre.
A wreath-laying is also planned at the Dryfesdale Cemetery.
In the evening, services will be held at Tundergarth and Dryfesdale churches.
Former Lockerbie councillor and eyewitness to the crash, Marjory McQueen, said residents of the town were well aware the anniversary would attract worldwide attention.
It is 20 years since Pan Am Flight 103 blew up over Lockerbie
It has become a place of pilgrimage for many people affected by events 20 years ago.
She said: "Now not only are we having people coming back again to Lockerbie who lost loved ones here, but we are having the second generation.
"Youngsters who were babes in arms and are now in their gap year or finished university want to come back and see where their mother, father, a relative or even a friend died."
Mrs McQueen said that the community recognised it was an emotional time for friends and family of the victims.
"Lockerbie moved on fairly rapidly after 1988 but there is always time for remembrance at this sort of anniversary," she said.
"The town will be warm and welcoming to people who want to come here at this time.
"There is more to Lockerbie now than just the disaster - but we live in the real world and know that this is a national and international event."
Mrs McQueen said she believed a close relationship had been built up between the town's inhabitants and people from further afield who had lost loved ones.
"I think the legacy of Lockerbie over the last 20 years has been the humanitarian side of what happened here," she said.
It is that bond which will be honoured by the ceremonies in the town on Sunday.
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