A nonprofit has no owners, which sounds like a technicality and is actually the organizing fact of the entire field. This article explains what follows from it: who the board answers to, why the state attorney general is a party in interest, and how fiduciary duties differ from their corporate analogues when there are no shareholders to sue. It covers the three duties that govern board service, the conflict-of-interest machinery that makes most transactions defensible, and the excess benefit rules that impose personal tax liability on insiders and on the board members who approved the deal. It then covers the annual filing that has become the sector's principal disclosure document, the tests that distinguish public charities from private foundations, and unrelated business income. It closes with the practical failures that cost organizations their exemptions.