This chapter discusses queens regnant and empresses regnant, women ruling in their own right. It is based on a provisional list of 27 cases. The earliest (in the frame of this book) are in Byzantium, Irene (797-802) and the sisters Zoe and Theodora in the eleventh century. The title of the latter is clearly seen as hereditary right, even though it seems that only slight efforts were made to ensure biological continuity of the dynasty. In contrast, the earliest western European case of a queen regnant, Urraca of Leon-Castile, shows how persistently her father sought to obtain a male heir, although he was willing to see her as his successor when he was left without one. The cluster of twelfth-century cases, Urraca, Melisende of Jerusalem and (ultimately unsuccessfully) Matilda. of England are analysed, and the issue of misogyny in the sources discussed. Female sovereigns are much more common in the Mediterranean and Iberian realms than further north. Though they are rarer in the thirteenth century than in the twelfth, fourteenth or fifteenth, this seems to have been purely circumstantial. The one explicit attempt to exclude women from succession, in late medieval France, is the result of one specific political crisis.