A legislative measure, designated "S. J. Res." and numbered consecutively upon introduction, which requires the approval of both chambers and, with one exception, is submitted (just as a bill) to the President for possible signature into law. The one exception is that joint resolutions (and not bills) are used to propose constitutional amendments. These resolutions require a two-thirds affirmative vote in each house but are not submitted to the President; they become effective when ratified by three-quarters of the States.
-  US Senate Reference