Final answer:
A two-thirds vote by both houses of Congress and a ratification vote of three-fourths of the states are required to amend the U.S. Constitution.
Step-by-step explanation:
The U.S. Constitution can be amended through a two-step process. Firstly, an amendment must be proposed by a two-thirds vote in both the House of Representatives and the Senate, or by two-thirds of state legislatures. Secondly, the amendment must be ratified by three-fourths of the state legislatures. This process ensures that amending the Constitution is a difficult and deliberate process.