By Helen Fawkes
BBC News, Kiev
For the first time as president of Ukraine, Viktor Yushchenko addressed his supporters.
Kiev city centre was one big orange party on Sunday
They were back on Kiev's Independence Square wearing orange scarves and waving orange flags.
"It's the greatest holiday today, we are so happy", said 67-year-old Volodymyr Gonchenko, who used to design computers for Soviet spacecraft.
Two months ago this was the scene of the opposition's orange revolution following a disputed November's poll.
This time people were here for a party not a protest.
"I took part every single day for 17 days that the protests lasted. We blockaded government buildings," said Mr Gonchenko.
Gonchenko says Yushchenko will now "fight for us"
"We fought for Yushchenko because we know he will fight for us."
Speaking to hundreds of thousands of Ukrainians, Mr Yushchenko thanked them for their part in getting him into power.
Mr Yushchenko - the former prime minister - won the re-run vote held last month.
Sparkling confetti in the Ukrainian colours of blue and yellow was pumped into the air for the celebrations.
Later the sky was filled with orange balloons as part of the celebrations.
"It seems like all our dreams have come true. For me it's one of the best things that has ever happened in my life and to Ukraine," said student Olga Didenko, 22.
Mr Yushchenko was flanked by delegations from around the world including US State Secretary Colin Powell.
Chervonenko says Yushchenko's triumph "is only the beginning"
Ukraine's third president was also accompanied by key opposition figures.
MP Yevhen Chervonenko has been at his side throughout the long and bitter election campaign.
"I am a strong man, but I cried when I saw my president and my friend Viktor on stage in Independence Square," admitted Mr Chervonenko.
"It's a great victory of Ukraine. I am delighted because this is a victory for all people from all parts of Ukraine."
As a symbol of peace, a number of white doves were released over the capital's main square.
Drive to Europe
Mr Yushchenko set out his vision for the future.
"My goal is for Ukraine to be in a united Europe. Europe holds Ukraine's historic chance to fulfil its potential."
"European standards will become the norm in public life, in the economy and in Ukrainian politics," Mr Yushchenko told his supporters.
Many people who voted for the opposition want to see their standard of living improve.
Ukraine is one of the poorest countries in Europe.
"It's not just a step but a leap from feudalism to democracy. We will now have a better future," said Oleg Komar, an office worker from Kiev.
The election campaign started last summer. It has been a long and bitter process.
"This is a historical day," Mr Chervonenko said.
"Not many people believed we could do it. This is only the beginning; we must continue to strive for a truly democratic and free Ukraine, because people have waited so long for change."