Alentejo is a south-central region of Portugal. It literally translates to "beyond the Tagus." The region is separated from the rest of Portugal by the Tagus river. It extends to the south where it borders the Algarve. There are four sub-regions; the Alto (High) Alentejo, the Baixo (Lower) Alentejo, the Alentejo Central, and the Alentejo Litoral. Its main cities are Évora, Portalegre, Beja, and Sines.

It has 776,585 inhabitantes (2001), and its area is about 26,000 km².

It is one of five Regions of Portugal (NUTS II subdivisions).

The area is commonly known as the "bread basket" of Portugal, a region of vast open countryside with undulating plains and rich fertile soil. With very few exceptions all the major towns are mainly reliant on agriculture, livestock and wood.

Topographically the countryside varies considerably, from the open rolling plains of the south of the Alentejo to the granite hills that border Spain in the north-east. To feed the water needs of this considerable area a number of public dams have been constructed.

To the east of Portalegre is the Parque Natural da Serra de São Mamede, a fascinating Nature Park Area that includes charming medieval villages that have changed very little from those days. In the south near Mértola is another Nature Park Area named Parque Natural do Vale Guadiana. This is mainly uninhabited and a contrast to the other above. To the west, the coastal strip that runs from the port of Sines down to Cape de São Vicente is also a reserved area.

Alentejo is a region known for its polyphonic singing groups, comparable to those found on Sardinia and Corsica.