Barack Obama has formally accepted the Democratic party's nomination to run for president of America in front of 80,000 people.
He told the crowd in a football stadium in Denver that the country would be better with him in charge than it had been under George Bush.
Mr Obama is the first ever black person to be chosen by a big party in America to run for president.
In the election, he'll have to beat the Republican candidate, John McCain.
Mr Obama told the cheering crowds on Thursday that he is the right man for the top job.
The two men hoping to be president
He said: "I will restore our moral standing, so that America is once again that last best hope for all who are called to the cause of freedom.
"This moment - this election - is our chance to keep, in the 21st Century, the American promise alive."
Mr Obama criticised Mr McCain, saying he is out of touch with the issues affecting ordinary Americans.
But afterwards, a campaign spokesman for Mr McCain hit back saying Mr Obama was still not ready to be president.
Senator McCain is expected to formally accept his nomination next week at his party's convention in Minnesota.