7 November 2012 Last updated at 13
Mr Obama congratulated Mr Romney and Republican vice-presidential candidate Paul Ryan on their hard-fought campaign.
"We have picked ourselves up, we have fought our way back and we know in our hearts that for the United States of America the best is yet to come," he said.
Mr Obama said he was returning to the White House "more determined, and more inspired than ever about the work there is to do, and the future that lies ahead".
He pledged to work with Republican leaders in Congress to reduce the government's budget deficit, fix the tax code and reform the immigration system.
"We are an American family and we rise and fall together as one nation," he said.
In Boston, where his campaign was based, Mr Romney congratulated the president and said he and Mr Ryan had "left everything on the field" and had given their all in the campaign. Hu vows to boost domestic demand, deepen economic reform
Hu Jintao on Thursday vowed to drive the economy more by domestic demand and push forward across-the-board economic reforms to address problems in the country.
