Alamannia, or Alemannia, was the kingdom established and inhabited by the Alemanni, a Germanic tribal confederation that had broken through the Roman limes in 213.

The Alemanni expanded from the Main River basin during the 3rd century and raided Roman provinces and settled on the left bank of the Rhine River from the 4th century.

Ruled by independent tribal kings during the 4th and the 5th centuries, Alamannia lost its independence and became a duchy of the Frankish Empire in the 6th century. As the Holy Roman Empire started to form under King Conrad I of East Francia (reigning 911 to 918), the territory of Alamannia became the Duchy of Swabia in 915. Scribes often used the term Suebia interchangeably with Alamannia in the 10th to the 12th centuries.

The territory of Alamannia as it existed from the 7th to 9th centuries centred on Lake Constance and included the High Rhine, the Black Forest and the Alsace on either side of the Upper Rhine, the upper Danube River basin as far as the confluence with the Lech River, with an unclear boundary towards Burgundy to the south-west in the Aare River basin (the Aargau). Raetia Curiensis, although not part of Alemannia, was ruled by Alemannic counts, and became part of the Duchy of Swabia since it was established by Burchard I (Duke of Alemannia from 909 to 911).

The territory corresponds to what is still the area of Alemannic German in the modern period, French Alsace, German Baden and Swabia, German-speaking Switzerland and the Austrian Vorarlberg.

In the area of present-day Switzerland, the Alemannic areal expanded during the High Middle Ages, with the Walser migration into the Alps, with the Zähringer and later the influence of Bern towards Upper Burgundy, and into Grisons as lower Raetia came under the rule of the Werdenberg counts.