First Lady of the United States is the unofficial title of the hostess of the White House. Because this position is traditionally filled by the wife of the President of the United States, the title is sometimes taken to apply only to the wife of a sitting President. However, several women who were not Presidents' wives have served as First Lady, as when the President was a bachelor or widower, or when the wife of the President was unable to fulfill the duties of the First Lady herself. In these cases, the position has been filled by a female relative or friend of the President.

To date, no woman has served as President. While a female President could theoretically serve as her own official hostess, it is not known what title would be applied to a President's husband, who might also serve as the host of the White House. There have been many female governors of U.S. states over the years; their spouses are typically referred to as the First Gentleman.

Senator Hillary Rodham Clinton of New York, wife of former president William Jefferson "Bill" Clinton, is the only spouse of a former president to be elected to the United States Senate. She is also the first spouse of a former president to run for the presidency in her own right. She is currently a candidate for the Democratic nomination for the 2008 Presidential election. If Senator Clinton wins the nomination and the general election, Bill Clinton would become the first person to serve in the capacity of First Gentleman of the United States.

The current First Lady is Laura Bush. In addition, there are currently five former First Ladies still living: Betty Ford, Rosalynn Carter, Nancy Reagan, Barbara Bush and Hillary Rodham Clinton.