President Sheikh Mohamed on Flag Day said people in the UAE are united by national pride and are optimistic about the future.
In a post on Twitter accompanied by a video showing UAE leaders with young Emiratis, Sheikh Mohamed said the optimism is based on the future generation who will continue the country's progress.
"As people across the UAE join together to raise the flag as one, we reflect on our country’s past and are optimistic for its future," he said.
"The UAE people are united by a shared sense of national pride and a steadfast belief in the next generation who will lead our continued progress."
Sheikh Mohammed bin Rashid, Vice President and Ruler of Dubai, shared a Twitter post with a group of Emirati boys.
"Today we raised the flag of the United Arab Emirates with a group of Emirati sons who represent part of our future," Sheikh Mohammed wrote.
"It's a day on which we establish loyalty and belonging in our generations and celebrate the symbol of our sovereignty and pride, and renew our pride in our unity and union. May God protect our flag, our state and our people."
The UAE celebrated Flag Day on Thursday, with schools and workplaces across the country marking the occasion.
At 11am, people briefly stopped work to mark the event, which is now in its 10th year.
It is commemorated every year on the anniversary, November 3, although the day is not a public holiday.
Who designed the UAE flag?
Abdullah Al Maainah came up with the design in 1971 as part of a competition run by Al Ittihad newspaper.
The young Emirati intended the four colours to represent Arab unity, as described in poetry written by Safi-u-ddin Al Hali.
His submission beat more than 1,000 entries vying to become the emblem of the new nation.
Mr Al Maainah was 19 at the time and would later become the minister of foreign affairs.
Only two flags were raised in December 1971 to mark the formation of the nation — one in Abu Dhabi and the other at Union House in Dubai.
On Thursday, there are likely to be hundreds of thousands.