How the Constitution can be amended

President Bush is urging Congress to approve a constitutional amendment banning gay marriage. Here's an outline of how the amendment process works:
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. Currently 38 states have a defense of marriage act (DOMA) law in place prohibiting marriage for same-sex couples.
The Constitution has been amended six times since the 1950s. The three most recent were:
-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 two most recent amendments that received congressional approval but failed to gain ratification by states were the Equal Rights Amendment and the District of Columbia Voting Rights Amendment.
The Equal Rights Amendment would have set into law equality between men and women. The period for states to ratify it expired in 1982.
The D.C. Voting Rights Amendment would have granted the capital city full representation in Congress instead of its one nonvoting member. The ratification period for the D.C. amendment expired in 1985.
Five amendments have been introduced in Congress since 2003, none of which have been acted on. They would:
-Guarantee the right to use the word "God" in the Pledge of Allegiance and the national motto.
-Restrict marriage in all states to between a man and a woman.
-Remove any protection any court may find for child pornography.
-Allow Congress to pass laws for emergency replenishment of its membership should more than one quarter of either the House or the Senate be killed.
-Place presidential nominees immediately into position, providing the Senate 120 days to reject the nominee before the appointment becomes permanent.