First Lady of the United States (FLOTUS) is the title held by the hostess of the White House, usually the wife of the president of the United States, concurrent with the president's term in office. Although the first lady's role has never been codified or officially defined, she figures prominently in the political and social life of the United States. Since the early 20th century, the first lady has been assisted by official staff, now known as the Office of the First Lady and headquartered in the East Wing of the White House.

Melania Trump is the current first lady of the United States, as wife of 45th president of the United States, Donald Trump. She will leave the role of First Lady on January 20, 2021 when Donald Trump leaves office.

While the title was not in general use until much later, Martha Washington, the wife of George Washington, the first U.S. president (1789–1797), is considered to be the inaugural first lady of the United States. During her lifetime, she was often referred to as Lady Washington.

Since the 1790s, the role of first lady has changed considerably. It has come to include involvement in political campaigns, management of the White House, championship of social causes, and representation of the president at official and ceremonial occasions. As first ladies now typically publish their memoirs, which are viewed as potential sources of additional information about their husbands' administrations, and because the public is interested in these increasingly independent women in their own right, first ladies frequently remain a focus of attention long after their husbands' terms of office have ended. Additionally, over the years individual first ladies have held influence in a range of sectors, from fashion to public opinion on policy. Historically, should a president be unmarried, or a widower, the president usually asks a relative or friend to act as White House hostess.

There are four living former first ladies: Rosalynn Carter, wife of Jimmy Carter; Hillary Clinton, wife of Bill Clinton; Laura Bush, wife of George W. Bush; and Michelle Obama, wife of Barack Obama.