Definition
The amendment process is the formal mechanism, set out in Article V of the U.S. Constitution, for altering the document itself. It is deliberately demanding: an amendment must clear two distinct stages, proposal and ratification, each requiring far more than a simple majority.
Because the bar is so high, only 27 amendments have been adopted in more than two centuries. The process treats the Constitution as a durable framework that should change rarely and only with broad, sustained agreement across the country.
Why it matters
How it works
There are two ways to propose an amendment and two ways to ratify one. Proposal happens either when two-thirds of both houses of Congress agree, or when two-thirds of state legislatures call for a national convention. Ratification then requires approval by three-fourths of the states, acting either through their legislatures or through specially elected conventions.
In practice, every amendment so far has been proposed by Congress, and all but one were ratified by state legislatures. The convention route remains untested, which keeps a degree of uncertainty around its exact procedures.