A stem duchy (German: Stammesherzogtum, from , meaning "tribe", in reference to the Germanic tribes of the Franks, Saxons, Bavarians and Swabians) was a constituent duchy of the kingdom of Germany at the time of the extinction of the Carolingian dynasty (the death of Louis the Child in 911) and the transitional period leading to the formation of the Holy Roman Empire later in the 10th century. The Carolingians had dissolved the original tribal duchies of the Frankish Empire in the 8th century. As the Carolingian Empire declined in the late 9th century, the old tribal areas assumed new identities as the subdivisions of the realm. These are the five stem duchies (sometimes also called "younger stem duchies" in reference to the pre-Carolingian tribal duchies): Bavaria, Franconia, Lotharingia, Saxony and Swabia (Alemannia). The stem duchies were retained as the major divisions of Germany under the Salian dynasty, but they became increasingly obsolete during the early high medieval period under the Hohenstaufen, and they were finally abolished in 1180 by Frederick Barbarossa in favour of more numerous territorial duchies.
The term Stammesherzogtum as used in German historiography dates to the mid-19th century, and from the beginning was closely related to the question of national unification. The term's applicability, and the nature of the stem duchies in medieval Germany consequently have a long history of controversy. The overly literal or etymologizing English translation "stem duchy" was coined in the early 20th century. While later authors tend to clarify the term by using the alternative translation "tribal", use of the term "stem duchies" has become conventional.