Mr Viktor Yushchenko became president of Ukraine today, ending weeks of turmoil and setting the stage for the ex-Soviet state to edge closer to Europe while upholding traditional links with Russia.
Mr Yushchenko read the oath of office with his hand on an ancient Bible and constitution during a parliament ceremony attended by hundreds of guests, including US Secretary of State Mr Colin Powell and presidents of seven countries.
Addressing parliament after being sworn in, Mr Yushchenko praised his hard-fought election win as a "national victory" today and urged deputies to work with him to build prosperity.
"The people achieved honest elections, the transfer of power was legitimate," Mr Yushchenko said after taking the oath of office.
"It is a great national victory." He praised parliament for helping defend his victory in last month's re-run of a rigged poll.
"Let me offer my hand to each of the deputies here... and ask for your cooperation. We have a single aim -- a democratic and prosperous Ukraine."
Shortly before becoming Ukraine's third president Mr Yushchenko (50) met Mr Powell while crowds gathered in the square decked in Yushchenko's orange campaign colours, trademark of the "Orange Revolution" that propelled him to power.
"I want to assure you that you will continue to enjoy the full support of the American government and the American people as you move forward to undertake the efforts that the Ukrainian people are expecting," Mr Powell told Yushchenko after their talks.
He said the meeting dealt with "activation of Ukrainian efforts toward international integration.
This includes the prospects for Ukraine acquiring a market-based economy." That, he said, was critical for Ukraine joining the World Trade Organisation.
Mr Yushchenko told Mr Powell he was happy "that I have lived to the time when the Ukrainian president is elected not in Moscow, not in Washington, but in Ukraine".
"This would not have happened if we didn't have partners that are advocating democratic principles and shared democratic values. And I certainly include in this list the United States of America and your personal contribution."