The Golden Horn (Turkish: Altın Boynuz or Haliç; Ancient Greek: Χρυσόκερας, Chrysókeras; Latin: Sinus Ceratinus) is a major urban waterway and the primary inlet of the Bosphorus in Istanbul, Turkey. As a natural estuary that connects with the Bosphorus Strait at the point where the strait meets the Sea of Marmara, the waters of the Golden Horn help define the northern boundary of the peninsula constituting "Old Istanbul" (ancient Byzantium and Constantinople), the tip of which is the promontory of Sarayburnu, or Seraglio Point. This estuarial inlet geographically separates the historic center of Istanbul from the rest of the city, and forms a horn-shaped, sheltered harbor that in the course of history has protected Greek, Roman, Byzantine, Ottoman and other maritime trade ships for thousands of years.

Throughout its history, the Golden Horn has witnessed many tumultuous historical incidents, and has been depicted in numerous works of art.

An hourly Golden Horn ferry service connects Üsküdar and Karaköy with most of the suburbs along the estuary. In 2021 the T5 tramline opened on the western shore of the Golden Horn. It runs from the Alibeyköy bus station as far as Cibali, beside the Atatürk Bridge, and an extension already in the making will continue it to Eminönü where it will intersect with the T1 tramline and several ferry services.