Tui is a municipality in the province of Pontevedra in the autonomous community of Galicia, in Spain. It is situated in the comarca of O Baixo Miño. It is located on the right bank of the Miño River, facing the Portuguese town of Valença. The municipality of Tui is composed of 11 parishes: Randufe, Malvas, Pexegueiro, Areas, Pazos de Reis, Rebordáns, Ribadelouro, Guillarei, Paramos, Baldráns and Caldelas.

Two bridges connect Tui and Valença: Tui International Bridge (known in Portugal as Valença International Bridge), completed in 1878 under the direction of Pelayo Mancebo, and a modern one from the 1990s. Both countries being signatories of the Schengen Treaty, there are normally no formalities in crossing what is the busiest border-point in northern Portugal.

Although Tui is just north of the border with Portugal, a shortened version of the Portuguese Way of the Camino de Santiago commences there, and as the distance is 116 kilometres (72 mi), this walk is long enough for pilgrims to obtain a pilgrim's certificate.