As of 2014, there are only 27 amendments successfully ratified to the U.S. Constitution. The first 10 amendments, known as the Bill of Rights, were submitted in 1789 and ratified in 1791. The last amendment to the Constitution came in 1993.
Many people have put forth efforts to add amendments to the U.S. Constitution with little success. More than 11,000 amendments have been proposed since 1793.
Although some of those amendments made it through Congress, they didn't receive the required number of votes from the states. Some of these failed amendments are still considered pending ratification, and could theoretically come to another vote by the states.