The river rises in the Montes Universales between Cuenca and Teruel, in mid-eastern Spain, flows 1,007 km (626 mi), generally westward, and empties into the Atlantic Ocean in Lisbon.

[2] The Tagus River originates at an elevation of 1,593 meters above sea level in a place known as Fuente García, within the municipality of Frías de Albarracín in Teruel, Spain.

[4] In Portugal, it flows for 145 km (90 mi) through the traditional regions of Beira Baixa, Alto Alentejo, Ribatejo, and Estremadura, which include the districts of Castelo Branco, Portalegre, Santarém, and Lisbon.

The most important cities along its course are Aranjuez, Toledo, and Talavera de la Reina in Spain; and Abrantes, Santarém, and Lisbon in Portugal.

The hydrological regime of the Tagus is determined by the rain and snow variations typical of the central region of the Iberian Peninsula, especially in reference to the mountain formations integrated here.

The banks and areas of influence of the Tagus are home to relevant flora and fauna, representative of the central region of the Iberian Peninsula.

The high degree of depopulation in some areas integrated into its basin, such as its upper and middle-lower course, has allowed the preservation of places of great ecological interest.

The nearly 100 km (60 mi) of the Alto Tajo canyon as it passes through the natural park of the same name offer one of the best options for practicing whitewater canoeing in the central peninsula.