Since the founding of America, the United States has ratified 27 amendments to the Constitution. The first ten, of course, form the Bill of Rights; subsequent amendments expanded rights for Black citizens and women, prohibited (and later repealed the prohibition on) the sale of alcohol, added presidential term limits and clarified presidential succession, abolished poll taxes and lowered the voting age, among other modifications. Background on each amendment can be found in the online treatise Constitution Annotated: Analysis and Interpretation of the United States Constitution.
For every amendment in the Constitution, though, there are thousands more that failed to complete the arduous ratification requirements outlined in Article V. (For details, see the 2016 Congressional Research Service report The Article V Convention to Propose Constitutional Amendments: Contemporary Issues for Congress.) The Amendments Project at Harvard University, launched on July 4, has compiled over 20,000 proposed amendments into a searchable database. Amendments Project director Jill Lepore, a professor of American History and law at Harvard, announced the archive in the New York Times, observing that "No one has ever taken stock of this history of failed amendments, an America that never was but was wanted by some, and sometimes by very many, or even most."
The Amendments Project also includes a Stories section, which contextualizes the amendment activity related to topics like abortion, the environment, the budget, religion, and marriage, among others. Stories are written by members of The Amendments Project research team. Explore the new Amendments Project database at its Search tab. Tips for searching the database are linked under Resources.
For more information about successful and proposed amendments, try a search of the Duke Libraries Catalog for "Constitutional Amendments – United States." You'll find e-books like Constitutional Amendments: Encyclopedia of the People, Procedures, Politics, Primary Documents relating to the 27 Amendments to the U.S. Constitution, John R. Vile's Conventional Wisdom: The Alternate Article V Mechanism for Proposing Amendments to the U.S. Constitution, and the late U.S. Supreme Court Justice John Paul Stevens's Six Amendments: How and Why We Should Change the Constitution. Print editions of these titles are also listed in the catalog.
For help with locating library materials about the Constitution and its amendments (successful or otherwise), be sure to Ask a Librarian.