Section 43(a)(1)(B) of the Lanham Act, 15 U.S.C. 1125(a), hands one business a federal weapon against a competitor's false or misleading advertising, and it has become the primary engine of business-to-business advertising disputes in technology markets, where claims are numeric, testable, and competitively decisive. This UpLaw research article works through the five elements, the standing framework the Supreme Court set in Lexmark v. Static Control, the outcome-determining split between literal and implied falsity, the necessary-implication doctrine, establishment versus non-establishment claims, the real limits of puffery, materiality, and the full remedies menu under Section 35. It explains why POM Wonderful v. Coca-Cola keeps the courthouse open even when a federal regulator polices the same claim, maps the recurring technology battlegrounds of cybersecurity absolutes, benchmark methodology, AI capability claims, and greenwashing under the FTC Green Guides, and compares litigation with the burden-flipped NAD self-regulatory track. A running hypothetical about a fictional database vendor keeps the doctrine concrete, and California and New York overlays round out the analysis for marketing and legal teams that want to make aggressive claims they can actually defend.