Alamannia or Alemannia is the territory inhabited by the Germanic Alamanni after they broke through the Roman limes in 213.

The Alamanni expanded from the Main basin during the 3rd century, raiding the Roman provinces and settling on the left bank of the Rhine from the 4th century.

Ruled by independent tribal kings during the 4th to 5th centuries, Alamannia loses its independence and became a duchy of the Frankish Empire in the 6th century, and with the beginning formation of the Holy Roman Empire under Conrad I in 911 becomes the Duchy of Swabia.

The term Swabia is often used interchangeably with Alamannia in the 10th to 13th centuries.The territory of Alamannia as it exists from the 7th to 9th centuries corresponds roughly to what is today the German region of Swabia, the French Alsace and the eastern part of the Swiss plateau (Eastern and Central Switzerland).The region of the Alamanni is always somewhat sprawling and comprises a number of different districts, reflecting its mixed origins.

In the Early Middle Ages, its territories are divided between the Diocese of Strassburg, which dates from about 614, the territory of Augusta Vindelicorum (Augsburg) from 736, the Moguntiacum (Mainz) archdiocese from 745, and of Basilia (Basel) from 805.

Its distinctive laws are codified under Charlemagne as the Duchy of Alamannia in Swabia.

Today the descendants of the Alamanni are divided between parts of four nations: France (Alsace), Germany (Swabia and parts of Bavaria), Switzerland and Austria, and the German spoken in those regions has distinctive regional dialects.