The Necessary and Proper Clause is one of the most important parts of the US Constitution. Today this short thirty-nine word paragraph is cited as the legal foundation for much of the modern federal government. Yet constitutional scholars have pronounced its origins and original meaning a mystery. Through three independent lines of research, the authors trace the lineage of the Necessary and Proper Clause to the everyday law of the Founding Era - the same law that American founders such as Madison, Hamilton, and Washington applied in their daily lives. Origins of the Necessary and Proper Clause are found in law-governing agencies, public administration, and corporations. Moreover, all of those areas were undergirded by common principles of fiduciary responsibility - reflecting the Founders' view that a public office is truly a public trust. This explains the choice of language in the clause and provides clues about its meaning. This book thus serves as a reference source for scholars seeking to understand the intellectual foundations of one of the Constitution's most important clauses.