The contestation surrounding the islands of Abu Musa, Greater Tunb, and Lesser Tunb (Three Islands) since the early twentieth century, intertwined with geopolitical shifts in the Persian Gulf and regional rivalries, has persisted in relations among Iran, certain Arab States, and Western powers. Employing an analytical approach and drawing upon a comprehensive body of cartographic evidence, diplomatic correspondence, foreign agents’ reports, administrative and maritime archives, official British positions, UN Security Council records, and the 1971 Memorandum of Understanding between Iran and Sharjah, this article argues that characterizations of the Iranian action on November 30, 1971, as an “illegal occupation” face formidable historical and legal hurdles. Findings demonstrate that pre-1903 archival records and circumstantial evidence not only reveal an absence of any clear basis for attributing these islands to rival political entities, but also, in numerous instances, affirmatively substantiate the administrative, territorial, and sovereign ties connecting these islands to Iran. From this perspective, British presence or intervention subsequent to 1903 cannot be construed as conferring an independent root of title upon the opposing party—particularly as such interventions were met with unbroken Iranian protests. Diplomatic démarches and persistent acts of protest by Iran from 1903 to 1971, coupled with the absence of valid consent or legally operative acquiescence, precluded rival claims from superseding Iran’s historical title through acquisitive prescription, implied recognition, or consolidation.