"I'm in," she said on a Web site, hillaryclinton.com. "And I'm in to win.
"As a senator, I will spend two years doing everything in my power to limit the damage George W. Bush can do," Clinton's statement added. "But only a new president will be able to undo Bush's mistakes and restore our hope and optimism."
While the timing of the news was a closely guarded secret, the announcement itself is not all together surprising. The junior senator from New York has been considering a presidential run for months.
During a televised debate just before her re-election to the Senate last November, Clinton told voters they should not count on her completing a full six-year Senate term.
Many political watchers consider Clinton the Democrat to beat - particularly given her prolific fundraising abilities. Associates of Clinton say she will be capable of raising tens of millions of dollars in the year to come.
Clinton enjoys a substantial early lead for the nomination. In an ABC News/Washington Post poll last month, she was supported by 39 percent of Democrats and Democratic-leaning independents, well ahead of her nearest competitors - Sen. Barack Obama, D-Ill., with 17 percent support; former Sen. John Edwards, D-N.C., with 12 percent; and former Vice President Al Gore, 10 percent.
Clinton's support is particularly strong among Democratic women; 49 percent favor her for the nomination, compared with 29 percent of Democratic men.
But Clinton herself has also frequently acknowledged that there will be a "vigorous debate" prior to the next presidential election. And Clinton will be anxious to distinguish herself from the other leading candidates - Obama and Edwards.
Source: ABC News