An intent-to-use filing lets a business claim a federal trademark before it has sold anything, holding its place in line as of the filing date while the product is still being built. This guide explains, for lawyers and founders alike, how the system converts a promise of nationwide rights into a reserved entitlement dating back to filing under the constructive-use rule of 15 U.S.C. § 1057(c). It works through the bona fide intent requirement and the objective, burden-shifting proof framework the courts and the TTAB apply; the full lifecycle from filing through the Notice of Allowance to the Statement of Use; the exact arithmetic of the extension deadlines; and the anti-trafficking rule that usually forbids selling an unused application. It closes with a start-to-finish worked launch, a field guide to the mistakes that sink applicants, an FAQ, and cross-references to the rest of the UpLaw trademark library.