The Tea Rose-Rectanus doctrine explains how two unrelated businesses can lawfully own the same trademark in different regions of the country. Rooted in two Supreme Court decisions from the 1910s, it treats a common-law mark as a local right tied to the markets where the owner actually trades and builds goodwill, so a later adopter who innocently uses the same mark in a separate, remote market can acquire its own rights there. This guide reconstructs the doctrine's origins, dissects its two elements of good faith and remoteness, works through the market-penetration proof that decides remoteness, and maps the live circuit split over whether mere knowledge of a senior user destroys good faith after Stone Creek v. Omnia. It then details how federal registration reshapes the picture going forward through constructive notice under 15 U.S.C. § 1072, constructive use under § 1057(c), and the frozen limited-area defense under § 1115(b)(5), including the Dawn Donut enforcement wrinkle. Multiple worked hypotheticals and a litigation-and-strategy section translate the doctrine into practice for registrants and unregistered owners alike.