In terms of constitutional law, early modern cities of the Holy Roman Empire are divided into imperial cities ("Reichsstadte") and provincial cities ("Landstadte"). While the former were directly subordinate to the Emperor and were represented in the Reichstag, a territorial ruler ("Landesherr") stood between the provincial cities and the head of the Empire. Since the 1980 s, a third category of cities has been considered in historical research, the so-called autonomous cities ("Autonomiestadte") in the north of the empire, which were de facto independent, but whose status was not based on imperial law. This study sheds light on this type of city and explores its characteristics. On the basis of contemporary treatise literature ("Reichspublizistik"), it is demonstrated that autonomous cities were already recognised as so-called civitates mixti status in the scholarly discourse of the early modern period. While they bore traits of imperial and provincial cities, they were closer to the former. By virtue of imperial privileges, they had imperial immediacy ("Reichsunmittelbarkeit"), but no imperial status ("Reichsstandschaft"), which they did not strive for. Using the example of the autonomous cities of Lower Saxony, especially the members of the Saxon League of Cities ("Sachsischer Stadtebund"), and the case study of the city of Einbeck, it is shown how the status of an autonomous city asserted itself in political practice and what the structural characteristics of this type of city were. In addition to membership of the Hanseatic League and regional alliances of cities, treaties with so-called patron princes ("Schutzfursten") were of great importance. With the autonomous cities, a facet of the early modern imperial constitution, that has received little attention so far, appears and deserves further attention from historical research.