This guide covers the liability of accountants and audit firms across every service they perform and every forum in which claims arise. It begins with the engagement types, because the assurance expressed determines the exposure, and works through audits, reviews, compilations, preparations, agreed-upon procedures, tax, and advisory work. It develops the privity rules that decide who may sue, comparing the near-privity, Restatement, and foreseeability approaches, and explains how the engagement letter bears on the knowledge element each requires. It covers the professional negligence standard and its defenses, then the federal securities framework, tracing why scienter, the absence of private aiding-and-abetting liability, and the maker requirement make auditors difficult for private plaintiffs to reach. It covers the public company oversight regime, independence, and internal control reporting; the absence of a federal accountant-client privilege and the limited protections that exist; the tax practice penalty and ethics regime; damages and the causation limits that shrink most claims; and claim strategy from both sides.