The Tournaisis (or Tournai and the Tournaisis) was a small territory in the Low Countries independent during the Middle Ages, consisting of the city of Tournai (Dutch: Doornik) and the surrounding area, which now forms part of Hainaut province in Belgium.
The Tournaisis was situated between two larger neighbours: the County of Flanders, and the County of Hainaut. Its origins lie in a Roman pagus within the civitas of the Menapii, of which it became the chief city in late Roman times. It had some independence and power in the Middle Ages because it became the seat of the Bishopric of Tournai.
The territory, like that of Flanders, but unlike neighbouring Hainaut, was part of early medieval West Francia, which evolved into France. However, this rule was not always effective. It came under French rule during the reign of Philip IV of France, and remained under French control until it was conquered by Emperor Charles V in 1521. It remained part of the Habsburg Netherlands until 1789, eventually becoming part of modern Belgium.
The Tournaisis was considered part of the Seventeen Provinces.