The amendments are changes or additions to the original written body of the U.S. Constitution. Article V of the Constitution stipulates how changes to the Constitution are made. There are 27 ratified amendments and six unratified or pending amendments, as of 2014.
Constitutional amendments can be proposed either by a two-thirds vote of both the Senate and House of Representatives or a constitutional convention convened by a consensus of at least two-thirds of the state legislatures. The president plays no part in the amendment process. Instead, once an amendment receives a necessary number of votes, the Office of the Federal Register sends the Congressional joint resolution and an information package to the state governors, who then pass the proposed amendment to the state legislatures for ratification.
An amendment is added to the Constitution when three-fourths of the states have ratified it. Sometimes Congress designates a time frame within which an amendment must be ratified, but other amendments are left open for ratification indefinitely. Some amendments are ratified within months, while others take a number of years. The 27th Amendment, dealing with congressional salaries, is the amendment with the longest ratification process, as of 2014, taking 202 years from proposal to ratification.
A number of states insisted on a definition of individual rights before ratifying the original body of the Constitution, so the first 10 amendments constitute the Bill of Rights. Other amendments clarify Supreme Court jurisdiction, abolish slavery, authorize tax on income and secure the rights of voters.