The President of the United States has the power to make treaties with foreign countries, but only with the advice and consent of the Senate. Under the U.S. Constitution, two-thirds of the Senate must consent to a treaty.
Treaties are not ratified by the Senate. Rather, the Senate votes either for or against a ratification resolution. As of February 2015, the Senate has approved most of the treaties on which it has voted. During the first 200 years of its existence, the Senate voted in favor of over 1,500 treaties and disapproved 21. Sometimes treaties are not even brought up for a vote, and many of these are eventually withdrawn. In other cases, a treaty will never make it out of the Senate Foreign Relations Committee for consideration by the full Senate.