Updated 4:32 p.m. - Hillary Rodham Clinton left the State Department on Friday"confident about the direction that we have set," handing off the secretary of state's job to former Sen. John Kerry, D-Mass.
Kerry took the oath of office, administered by Supreme Court Jusice Elena Kagan, late Friday afternoon. The private ceremony was closed to reporters.
The 2004 Democratic presidential nominee takes over for Clinton, who resigned her position hours earlier after a four-year term as America's top diplomat.
In remarks at the diplomatic agency's Foggy Bottom headquarters, Clinton waxed about the familiar atmosphere at the State Department during her four years as secretary, an environment she said would extend to Kerry.
In remarks at the diplomatic agency's Foggy Bottom headquarters, Secretary of State Hillary Rodham Clinton formally resigned her post at the State Department. Watch her entire statement.
"Next week, I would expect that all of you will be as focused and dedicated for Secretary Kerry as you have been for me, and that you will continue to serve President Obama and our nation with the same level of professionalism and commitment that I have seen firsthand," she told throngs of department staff gathered for her remarks.
Clinton leaves office at the height of her popularity, and amid intrigue about what her political future might hold. She remained as coy as ever about her future intentions, making no reference toward that, and focusing her remarks instead on the diplomatic corps.
"I will be an advocate, from the outside, for the work that you continue to do here, and at [US]AID," she said.
"I am more optimistic today than when I was when I stood here four years ago. Because I have seen, day after day, the contributions our diplomats and development experts are making," she also said, later adding: "I leave this department confident about the direction that we have set."
Kerry was set to be sworn into office in a private ceremony later on Friday afternoon, and he'll inherit a number of complex foreign policy issues when he does.
Included among those vexing issues is the apparent terrorist attack against a U.S. Embassy in Ankara, Turkey on Friday. Clinton, in her valedictory remarks, said that she had spoken to the ambassador to Turkey, and acknowledged the loss of "one of our foreign service nationals" in the attack.