A trademark cease-and-desist letter is the most consequential low-cost move a brand owner makes, and the difference between a letter that quietly ends a dispute and one that starts a lawsuit is almost entirely drafting and judgment. This guide walks the full arc: auditing your own priority, scope, and strength before you accuse anyone; running an honest likelihood-of-confusion analysis under the circuit multifactor tests; picking a tone matched to your actual goal; and assembling the letter section by section. It maps the two hazards that ambush careless senders — declaratory-judgment jeopardy under MedImmune v. Genentech, which can flip you into a defendant in a distant forum, and the reputational backlash of "trademark bullying" and the Streisand effect. It grounds every threat in the remedies the Lanham Act actually authorizes after Romag and the Trademark Modernization Act, supplies an annotated model outline and a fully worked hypothetical, and closes with a detailed FAQ and cross-references to the rest of the UpLaw trademark library. It is written so a business owner, in-house counsel, a litigator, and a judge can all follow it.