The monarch welcomed the American president in the courtyard of the royal castle.
A military band honored Trump with a Royal Salute before playing the U.S. National Anthem.
Trump and the queen are set to inspect the assembled honor guard before viewing a military "march past." The Trumps and the queen are scheduled to spend about 30 minutes getting acquainted over tea inside the castle.
Friday morning, demonstrators took to the streets outside the Parliament to mock Trump as a giant balloon depicting him as a screaming orange baby flew over the area.
WATCH: Demonstrators in London mock President Trump with giant balloon over Parliament