A plain-English, deeply sourced FAQ on United States advertising law written for small-business owners, founders, marketers, and the general-practice lawyers who advise them. It starts with Section 5 of the FTC Act and its demand that advertising be truthful, substantiated, and fair, then works through the doctrines that catch real companies off guard: the reasonable-basis rule, express versus implied and monadic versus comparative claims, the reasonable-consumer and net-impression tests, the 2023 endorsement and influencer Guides, the 2024 fake-review rule, native advertising, Made in USA, the Green Guides, deceptive pricing, free offers, and bait-and-switch. It maps the statutes that govern how you reach customers, including CAN-SPAM for email, the TCPA for texts and robocalls, the Telemarketing Sales Rule, COPPA for children, and the negative-option and dark-pattern rules for subscriptions. It covers competitor disputes under Lanham Act Section 43(a) and the self-regulatory route through the National Advertising Division, and it flags where federal law becomes a floor beneath the fifty-state patchwork of consumer-protection statutes. Worked hypotheticals illustrate each rule in concrete terms a non-lawyer can follow.