The River Boyne is a river in Leinster, Ireland, the course of which is about 112 kilometres (70 miles) long. It rises at Trinity Well, Newbury Hall, near Carbury , County Kildare, and flows towards the Northeast through County Meath to reach the Irish Sea at Drogheda. Salmon and trout can be caught in the river, which is surrounded by the Boyne Valley. It is crossed just west of Drogheda by the Boyne River Bridge.

Despite its short course, the Boyne has historical, archaeological and mythical connotations. It passes near the ancient city of Trim, Trim Castle, the Hill of Tara (the ancient capital of the High King of Ireland), Navan, the Hill of Slane, Brú na Bóinne (an archaeological site), Mellifont Abbey, and the mediaeval city of Drogheda. In the Boyne Valley can also be found other historical and archaeological monuments, like Loughcrew, Kells, Celtic crosses, castles, and more. The Battle of the Boyne took place near the banks of the Boyne in 1690.

This river has been known since ancient times. The Greek geographer Ptolemy draw a map of Ireland in the 2nd century which included the Boyne, which he called Bovinda, and somewhat later Giraldus Cambrensis called it Boandus. Referring to legendary stories, it was in this river where Fionn mac Cumhail captured Fiontán, the Salmon of Knowledge. It was also said that the river was named after the goddess Boann ('queen' or 'goddess'), according to F. Dinneen, lexicographer of the Irish Gaelic language, and Boyne is an anglicised form of the name.