Here's a timely article describing the process for amending the Constitution:

The Constitution provides that an amendment can be proposed either by Congress with a two-thirds majority vote in both the House and Senate, or by a constitutional convention called for by two-thirds of the state legislatures. So far, none of the 27 amendments to the Constitution has been proposed by constitutional convention.

In the case of a congressional vote, after passage in the form of a joint resolution, the archivist of the United States submits the proposed amendment to the states for their consideration. A proposed amendment becomes part of the Constitution if it is ratified by three-fourths, or 38, of the 50 states.

The Consitution has been amended six times since the 1950's. Here are the last three, from the same article

• The 27th Amendment, ratified in 1992, to prevent Congress from passing a law giving itself a pay raise before the next election.

• The 26th Amendment, in 1971, which extended the right to vote to citizens as young as 18.

• The 25th Amendment, ratified in 1967, which set out rules for the transfer of presidential power to the vice president in case the president is unable to fulfill the duties of the office.

The last two amendments that had congressional approval (the Equal Rights Amendment and the D.C. Voting Rights Amendment) failed to pass before the expiration of their respective ratification deadlines.