A Quorum is the minimum number of House members or Senators that must be present before business may be conducted. A quorum in the House requires the presence of 218, while 100 are needed in Committee of the Whole. The Constitution requires 51 Senators for a quorum. Often, fewer Senators are actually present on the floor, but the Senate presumes that a quorum is present unless the contrary is shown by a roll call vote or quorum call.