The Mureş (Romanian Mureş; Hungarian Maros) is an approximately 761 km (473 mi) long river in Eastern Europe. It originates in the Hăşmaşu Mare Range in the Eastern Carpathian Mountains, Romania, and joins the Tisza river at Szeged in southeastern Hungary.

The Mureş River flows through the Romanian counties Harghita, Mureş, Alba, Hunedoara and Arad, and the Hungarian county Csongrád. The largest cities on the Mureş/Maros are Târgu Mureş and Arad in Romania and Szeged in Hungary.

The Mureş was known as the river Marisus in antiquity. It was also known in German as the Mieresch and Marosch owing to Transylvanian Saxon settlements and one-time Austrian Habsburg rule. Salt used to be traded in medieval times on the river on large rafts.

The Hungarian reaches of the Mureş/Maros are 73 km long (22.3 km as the state border). Some 28.5 km² on the northern side of the river are protected as part of the Körös-Maros National Park. The Maros Floodplain Protected Area consists of gallery forests, floodplain meadows and 0.6 km² of forest reserve near Szeged.

The following towns are situated along the river Mureş, from source to mouth: Topliţa, Reghin, Târgu Mureş, Luduş, Ocna Mureş, Aiud, Teiuş, Alba Iulia, Geoagiu, Orăştie, Simeria, Deva, Lipova, Arad, Nădlac (all in Romania), Makó, Szeged (both in Hungary).

The following rivers are the major tributaries to the river Mureş: Arieş, Niraj, Sebeş, Strei and Târnava.