The 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.

Jill Biden is the current first lady of the United States, as wife of the 46th and current president of the United States, Joe Biden.

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 1900s, 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, as well as advocacy for female empowerment. Historically, should a president be unmarried or a widower the president usually asks a relative to act as White House hostess.