Sundgau (French pronunciation: [suŋɡo][1][2] or [syŋɡo];[3][4] German: [ˈzʊntɡaʊ]) is a geographical territory in the southern Alsace region (Haut Rhin and Belfort), on the eastern edge of France.

The hilly region is bounded on the south by the Swiss border and the foothills of the Jura, in the east by the valley of the Rhine in the vicinity of Basel, to the north by Mulhouse and the potassium-rich basin of Alsace, and to the west by the Belfort Gap.

It comprises parts of the modern Department of Haut-Rhin and the Territory of Belfort in the regions of Alsace and the Franche-Comté.

The fertile loess soil has traditionally favoured a non-specialised agriculture, with crop production being largely organised into strips.

Other rivers define the region's valleys, such as the Largue, which rises near Courtavon, passes through Dannemarie, and meets the Ill at Illfurth.

In the 1st century BC, the Sequani tribe (the most "Gaulish of Gauls" according to historian Henri Martin), which was centered around Besançon, settled in Sundgau.

From 70 BC, they waged perpetual warfare with their neighbours, the Aedui, calling upon German mercenaries, led by Ariovistus.

About 750, the Duchy of Alsace was divided into two counties: Nordgau (Unterelsass) and Sundgau, the latter being mentioned in the Treaty of Mersen in 870.

Historically then, Sundgau coincides with the lands of the counts of Ferrette and Habsburg, excepting the town of Mulhouse and its territories of Illzach and Modenheim [fr].

Geographically, Sundgau denotes a more restricted area comprising the hilly country to the south of Mulhouse and reaching to the valley of Lucelle.

Following the breakup of Charlemagne's empire, the region entered a period of instability, culminating in the emergence of feudalism.

The Habsburgian Sundgau was administered from Ensisheim by a bailli (bailiff or seneschal) and divided into four bailiwicks (Landser, Thann, Altkirch and Ferrette).

Commencing in 1632, the Thirty Years' War broke upon Sundgau, with a violence unprecedented in the history of the region.

The country, only German speaking at that time, was conquered and annexed by France, and in 1659, the counthood of Ferrette was granted to Cardinal Mazarin (nominally by the then 21-year-old Louis XIV).

In 1789, the repercussions of the French Revolution reached Sundgau, and many conflicts arose in the townships, mainly due to the unpopularity of the ruling classes.

Little changed during the 19th century, agriculture remaining the principal economic activity, despite the establishment of industries such as the Gilardoni tileworks in 1835 and the construction of Xavier Jourdains' looms in Altkirch.

As a result of the 1870 Franco-Prussian War, Sundgau returned to Germany as part of the Imperial territory of Alsace-Lorraine.

Sundgau reverted to France in 1918, but its reintegration posed several problems; since Alsace was German speaking, they now saw themselves obliged to express themselves in French.

Qualifications are lower and revenues higher as a result of border area employment and its economic and social impact.

Although several enterprises have started during the last ten years, it is not sufficiently attractive as an employment basin because of the counterattractions of the nearby conurbations.

The General Council of Haut-Rhin has taken an interest in Sundgau and in developing tourism in the region since 2000, along the lines of the management of the source of the Ill or the construction of a rest area on the route D419 near Chavannes-sur-l'étang.

Sundgau is a region where the lifestyle permits the development of Green Tourism (i.e. where the visitor seeks calm, wishes to be in direct contact with nature, and has activities such as countryside walks and drives available).