This book presents and examines the purpose and activities of Congressional Member Organizations (CMOs) and the reasons Members form them, with a focus on identifying and describing the seven CMO types. Also discussed is the historical development of informal Member organisations since the first Congress, focusing on their regulation in the House by the Committee on House Oversight/Committee on House Administration; the rise and fall of legislative service organisations; and the House's decision to issue regulations for establishing CMOs and governing their behaviour.