Section 512 of the Digital Millennium Copyright Act runs almost all online copyright enforcement through a private, judge-free procedure: a compliant notice forces a hosting provider to remove material to preserve its safe harbor, and a compliant counter-notice forces the material back unless the rights holder files suit inside a two-week window. This article works both sides of that transaction. It maps the four safe harbors of Section 512(a)-(d), the four conditions of the Section 512(c) hosting harbor, and the Section 512(i) repeat-infringer gate that quietly decides the largest cases. It walks the six elements of a takedown notice and the five elements of a counter-notice, with annotated models, and explains the deficiencies that make providers ignore bad notices. It covers the specific-knowledge and red-flag standards of Viacom v. YouTube, the reasonable-implementation rule that cost Cox its harbor in BMG v. Cox, the knowing-misrepresentation standard of Section 512(f) and the fair-use duty of Lenz v. Universal, and the Section 512(h) subpoena. It closes with platform-specific practice, the EU Digital Services Act and Copyright Directive, the reform debate, and a practitioner FAQ. Written for creators, platforms, and counsel on either side of the notice.