More than five decades of Cold War and lingering enmity have come to an end with the United States and Cuba restoring full diplomatic relations.
The new era of US-Cuba relations began with little fanfare at midnight in Washington and Havana, when an agreement to resume full ties came into force.
In Monday's pre-dawn hours, the Cuban flag will be hung quietly in the lobby of the State Department alongside those of other nations with which the US has diplomatic relations.
Meanwhile, for the first time since 1961 the Cuban flag will fly over Havana's newly upgraded embassy in Washington, just a stone's throw from the White House.
The shift will be publicly memorialised later on Monday when Cuban officials formally reopen the embassy.
Secretary of State John Kerry will then meet his Cuban counterpart and address reporters at a joint news conference.
A foreign policy legacy for US President Barack Obama, the historic turnaround between two bitter foes has come about in just a matter of months.
The shift came after Washington acknowledged that its policy of trying to affect change in tightly controlled communist Cuba through isolation and trade restrictions had failed, and that engaging Havana directly was a better way to nudge it towards democracy and prosperity.