A Member of Congress endorses a bill introduced by another Member by “signing on” to it. Some cosponsors work as hard to promote a bill as the original sponsor; others just lend their name as a supporter.

A legislator who joins with the primary sponsor to guide a bill or resolution through the legislative process in the opposite chamber. A cosponsor must be a member of the opposite chamber from the one in which the bill was filed.

sponsor together with another sponsor