It's possibly the most recognizable workspace in the world, but the office that President-elect Barack Obama, its next occupant, visited on Nov. 10 hasn't always been the enduring symbol of the U.S. presidency. Before the 1930s, the Oval Office was in a different part of the White House. And before that, it wasn't even oval.

In 1902, Theodore Roosevelt built a rectangular room on the ground floor of the new West Wing, replacing offices on the second floor of the White House. William Howard Taft made it into an oval in honor of a symbolic feature of George Washington's Philadelphia residence: a room with a bowed end where the first President would stand surrounded by a circle of guests, allowing him to democratically greet each visitor from the same distance. The office was moved to its current location in the southeast corner of the White House in 1934.

Presidents since have left their mark on the office (except Jimmy Carter, who kept Gerald Ford's décor). L.B.J. installed a bank of televisions. On the Resolute desk, used by 21 of the past 24 Presidents, Harry Truman placed his THE BUCK STOPS HERE SIGN (the reverse read I'M FROM MISSOURI). And while its darker hours saw Richard Nixon's secret taping sessions and, in adjoining rooms, Bill Clinton's trysts with Monica Lewinsky, the Oval Office is where the President comes to draw the nation together--as Ronald Reagan did after the Challenger disaster, or George W. Bush after 9/11.