Tiber (Latin, Tiberis; Italian Tevere), river in central Italy, third longest of the country, rising in the Apennines of central Italy, near the source of the Arno River. It flows south in a picturesque, winding course across Umbria and then south-west through Latium, to empty via a delta in the Tyrrhenian Sea near Rome. The Tiber delta has two channels: the Fiumara, which enters the sea near the site of the ancient port city of Ostia, and the Fiumicino, an artificial waterway used by ships. The Tiber is about 404 km (251 mi) long; the principal cities on its banks are Città di Castello, Rome, and Todi.

The main tributaries of the Tiber are the Nera and Aniene rivers. The Tiber deposits much silt near its mouth, and navigation here is only possible with frequent dredging. Smaller craft are able to use the river from the sea to the confluence of the Nera, about 80 km (50 mi) north of Rome.