The Founding Fathers of the United States, referred to as the Founding Fathers or the Founders by Americans, were a group of late-18th-century American revolutionary leaders who united the Thirteen Colonies, oversaw the War of Independence from Great Britain, established the United States of America, and crafted a framework of government for the new nation.

The Founding Fathers include those who wrote and signed the United States Declaration of Independence, the Articles of Confederation, and the Constitution of the United States, certain military personnel who fought in the American Revolutionary War, and others who greatly assisted in the nation's formation. The single person most identified as Father of the United States is George Washington, commanding general in the American Revolution and the nation's first president. In 1973, historian Richard B. Morris identified seven figures as key founders, based on what he called the "triple tests" of leadership, longevity, and statesmanship: John Adams, Benjamin Franklin, Alexander Hamilton, John Jay, Thomas Jefferson, James Madison, and Washington.

Most of the Founding Fathers had ancestry traceable back to England, though many had family roots extending across the other regions of the British Isles: Scotland, Wales, and Ireland. Additionally, some traced their lineage back to the early Dutch settlers of New York (New Netherland) during the colonial era, while others were descendants of French Huguenots who settled in the British Thirteen Colonies, escaping religious persecution in France. Many of them were wealthy merchants, lawyers, landowners, and slaveowners.

Historian Richard Morris' selection of seven key founders was widely accepted through the 20th century. John Adams, Thomas Jefferson, and Benjamin Franklin were members of the Committee of Five that were charged by the Second Continental Congress with drafting the Declaration of Independence. Franklin, Adams, and John Jay negotiated the 1783 Treaty of Paris, which established American independence and brought an end to the American Revolutionary War. The constitutions drafted by Jay and Adams for their respective states of New York (1777) and Massachusetts (1780) proved influential in the language used in developing the U.S. Constitution. The Federalist Papers, which advocated the ratification of the Constitution, were written by Alexander Hamilton, James Madison, and Jay. George Washington was commander-in-chief of the Continental Army and later president of the Constitutional Convention.

Each of these men held additional important roles in the early government of the United States. Washington, Adams, Jefferson, and Madison served as the first four presidents; Adams and Jefferson were the nation's first two vice presidents; Jay was the nation's first chief justice; Hamilton was the first secretary of the treasury; Jefferson was the first secretary of state; and Franklin was America's most senior diplomat from the start of the Revolutionary War through its conclusion with the signing of the Treaty of Paris in 1783.

The list of Founding Fathers is often expanded to include the signers of the Declaration of Independence and individuals who later approved the U.S. Constitution. Some scholars regard all delegates to the Constitutional Convention as Founding Fathers whether they approved the Constitution or not. In addition, some historians include signers of the Articles of Confederation, which was adopted in 1781 as the nation's first constitution.

Historians have come to recognize others as founders, such as Revolutionary War military leaders as well as participants in developments leading up to the war, including prominent writers, orators, and other men and women who contributed to cause. Since the 19th century, the Founding Fathers have shifted from the concept of them as demigods who created the modern nation-state, to take into account their inability to address issues such as slavery and the debt owed after the American Revolutionary War. Scholars emphasize that the Founding Fathers' accomplishments and shortcomings be viewed within the context of their time.

The phrase "Founding Fathers" was first used by U.S. senator Warren G. Harding in his keynote speech at the Republican National Convention of 1916. Harding later repeated the phrase at his March 4, 1921, presidential inauguration. While U.S. presidents used the terms "founders" and "fathers" in their speeches throughout much of the early 20th century, it was another 60 years before Harding's phrase would be used again during the presidential inaugural ceremonies. Ronald Reagan referred to "Founding Fathers" at both his first inauguration on January 20, 1981, and his second on January 20, 1985.