In the Senate, a Senator who has the floor can force a quorum call at almost any time by suggesting the absence of quorum. The presiding officer usually cannot count to determine whether or not a quorum is present. So when a Senator "suggests the absence of a quorum," the presiding officer directs the Clerk to call the roll of Senators aloud by name. If a majority of Senators respond, a quorum is present and the Senate can return to its business.

However, a quorum call in the Senate usually has a different purpose: most often it is a strategic move that is used to delay proceedings for a variety of reasons -- for example, to conduct informal negotiations on or off the Senate floor, or to await a Senator who is expected to make a speech or propose an amendment. If the purpose of a quorum call actually is to bring a majority of Senators to the floor, it is known as a "live" quorum call.

A quorum call in the House seeks to bring a majority of Members to the floor to record their presence after the absence of a quorum has been established. In the House, a Member makes a point of order that a quorum is not present, usually only when a vote is taking place. The Speaker (or the Chairman of the Committee of the Whole) then counts to determine if a quorum is present. If a majority of Members fail to respond to a quorum call, the House must adjourn or take steps to secure the attendance of enough Members to constitute a quorum.

By long-standing practice, both the House and Senate normally presume that a quorum is present. Since a quorum is assumed, much of the business of Congress takes place -- even the passage of bills -- when only a small number of Members is present on the floor.