Modern republicanism is a guiding political philosophy of the United States that has been a major part of American civic thought since its founding. It stresses liberty and inalienable individual rights as central values; recognizes the sovereignty of the people as the source of all authority in law; rejects monarchy, aristocracy, and hereditary political power; expects citizens to be virtuous and faithful in their performance of civic duties; and vilifies corruption. American republicanism was articulated and first practiced by the Founding Fathers in the 18th century. For them, "republicanism represented more than a particular form of government. It was a way of life, a core ideology, an uncompromising commitment to liberty, and a total rejection of aristocracy."

Republicanism was based on Ancient Greco-Roman, Renaissance, and English models and ideas. It formed the basis for the American Revolution, the Declaration of Independence (1776), the Constitution (1787), and the Bill of Rights, as well as the Gettysburg Address (1863).

Republicanism includes guarantees of rights that cannot be repealed by a majority vote. Alexis de Tocqueville warned about the "tyranny of the majority" in a democracy and suggested the courts should try to reverse the efforts of the majority to terminate the rights of an unpopular minority.

The term 'republicanism' is derived from the term 'republic', but the two words have different meanings. A 'republic' is a form of government (one without a hereditary ruling class); 'republicanism' refers to the values of the citizens in a republic.

Two major parties have used the term in their name – the Democratic-Republican Party of Thomas Jefferson (founded in 1793, and often called the 'Jeffersonian Republican Party'), and the current Republican Party, founded in 1854 and named after the Jeffersonian party.