A crown prince is the male heir apparent to the throne in a royal or imperial monarchy. The female form of the title is crown princess, which may refer either to an heir apparent or, especially in earlier times, to the wife of the person styled crown prince.
Crown prince as a descriptive term has been used throughout history for the prince who is first-in-line to a throne and is expected to succeed (i.e. the heir apparent), barring any unforeseen future event preventing this. In certain monarchies, a more specific substantive title may be accorded and become associated with the position of heir apparent (e.g. Prince of Wales in the United Kingdom). In these monarchies, the term crown prince may be used less often than the substantive title (or never).
Until the late twentieth century, no modern monarchy adopted a system whereby females would be guaranteed to succeed to the throne (i.e. absolute primogeniture). A crown princess would therefore be more likely to refer to the spouse of a crown prince. She would be styled crown princess, not in her own right but by courtesy.
The term crown prince is not used in monarchies wherein the hereditary sovereign holds a title below that of king/queen or emperor/empress (such as grand duke or prince), although it is sometimes used as a synonym for heir apparent.
In Europe, where primogeniture governed succession to all monarchies except those of the Papacy and Andorra, the eldest son or (more recently) eldest child of the current monarch fills the role of crown prince or princess, depending upon whether females of the dynasty enjoy personal succession rights. Primogeniture has been abolished in Belgium, Denmark, Luxembourg, Norway, Sweden, the Netherlands and the United Kingdom. The eldest living child of a monarch is sometimes not the heir apparent or crown prince, because that position can be held by a descendant of a deceased older child who, by "right of representation", inherits the same place in the line of succession that would be held by the ancestor if he or she were still living (for example, Carl Gustaf, Duke of Jämtland was the crown prince of Sweden from 1950 to 1973, as the senior grandson by male primogeniture of King Gustaf VI Adolf of Sweden, although the former Prince Sigvard, Duke of Uppland was Gustaf VI Adolf's eldest living son, and Prince Bertil, Duke of Halland his eldest living dynastic son during those years).
In some monarchies, those of the Middle East for example, in which primogeniture is not the decisive factor in dynastic succession, a person may not possess the title or status of crown prince by right of birth, but may obtain (and lose) it as a result of an official designation made on some other legal or traditional basis, such as former crown prince Hassan bin Talal of Jordan.
Compare heir apparent and heir presumptive. In Scandinavian kingdoms, the heir presumptive to the crown may hold a different title than the heir apparent: hereditary prince (German: Erbprinz, French: prince héréditaire). It is also the title borne by the heir apparent of Liechtenstein, as well as the heir apparent or presumptive of Monaco. In Luxembourg, the heir apparent bears the title of hereditary grand duke (German: erbgroßherzog, Luxembourgish: ierfgroussherzog); along with hereditary prince, it was also the title borne by the heirs apparent to the thrones of the grand duchies, sovereign duchies and principalities, and of mediatized princely families in the German monarchies abolished in 1918.
Many monarchies use or did use substantive titles for their heirs apparent, often of historical origin:
Some monarchies have used (although not always de jure) a territorial title for heirs apparent which, though often perceived as a crown princely title, is not automatically hereditary. It generally requires a specific conferral by the sovereign, which may be withheld.
Currently, the following states use the term "crown prince" (or "crown princess") for the heirs apparent to their thrones:
In addition; the following heirs apparent to deposed monarchies use the title of Crown Prince as a title used by international courtesy: