THE UNITED STATES Congress is the oldest democratic legislature in the world, having been in continuous operation since the late 1700s. It is also the most influential legislature in the world. As the lawmaking branch of the most powerful nation on earth, Congress regularly makes decisions that affect not only the United States, but also the economies and security of many other nations.

Congress is a democratic body because its members are elected by and represent the American people. Representatives and senators, collectively referred to as members of Congress, each have their individual constituencies—the people who elected them. Members of Congress meet, debate, and vote on issues that affect both their constituents' local interests and the interests of the nation as a whole. In performing these functions, Congress, like the other two branches of the government—the...