The HeinOnline United States Congressional Serial Set, commonly referred to as the Serial Set, is considered an essential publication for unveiling American history. Spanning more than two centuries with more than 17,000 bound volumes, the records in this series include House and Senate Documents, House and Senate Reports, and much more. The reports are usually from congressional committees dealing with proposed legislation and issues under investigation. The documents include all other papers ordered printed by the House or Senate. Documents cover a wide variety of topics, including reports of executive departments and independent organizations, reports of special investigations made for Congress, and annual reports of non-governmental organizations. During the late nineteenth and early twentieth centuries, executive-branch materials were also published in the Serial Set.