A queen regnant (plural "queens regnant") is qualifying reference to a female monarch possessing and exercising all of the monarchal powers of a ruler, in contrast with a "queen consort", who is the wife of a reigning king as monarch, and in and of herself has no official powers of state. The term is redundant in cultures or countries where a queen always ruled as the monarch when bearing the title queen or where the wife of a king bore another title than queen, when having no official powers.
Technically, a king also may be a "king regnant" or a "king consort"—but this distinction is unusual and, for example, has been used only twice in the history of the British and its predecessor monarchies. In all current monarchies that allow for a queen to take the Throne, the husband of such a queen is not titled king, generally ranking as a prince. The husband of Mary I of England and Ireland and the second husband of Mary I, Queen of Scots were both created kings consort of their wives' realms. The husband of Mary II, Queen of England and Ireland, and Queen of Scots, was named king regnant co-sovereign with her, as William III of England, II of Scots, and I of Ireland—but this was the only occasion of co-sovereignty in Britain, at least officially. Thereafter, the husbands of queens regnant in Britain have been informally styled princes consort (the formal title Prince Consort, however, having been granted only to Prince Albert, the husband of Queen Victoria).
Accession of a regnant occurs as a nation's order of succession permits. Methods of succession (to queendoms, kingdoms, tribal chiefships, etc.) include nomination (the sitting monarch or a council names an heir), primogeniture (children of a monarch or chief, in order of birth, eldest to youngest), and ultimogeniture (children in order of birth, youngest to eldest). The scope of succession may be matrilineal, patrilineal, or both; or, rarely (usually only when necessary), open to general election. Right of succession by gender may be open to men and women, limited to men only, or limited to women only.
The most typical succession in European monarchies from the Late Middle Ages through to the twentieth century was male-preference primogeniture; i.e., the order of succession cycled through the sons of the monarch in order of their birth, followed then by the daughters. Many realms historically forbade succession by women or through a female line, however, in obedience to the Salic law; and some still do. No Queen Regnant ever ruled France, for example, nor, the Holy Roman Empire if one excepts Maria Theresa, who held the title of, HIM The Holy Roman Empress and was the de facto ruler. The Chrysanthemum Throne of Japan is currently barred to women, although historically, this has not always been the case.
In the waning days of the twentieth century, Sweden, Norway, Belgium, and the Netherlands amended their acts of succession to primogeniture with no preference as to sex. In some cases, the change does not take effect until the generation following the current generations in existence - to avoid dispossessing people who were already in the succession in a particular position.
