An heir apparent or simply heir is a person who is first in an order of succession and cannot be displaced from inheriting by the birth of another person. A person who is first in the current order of succession but could be displaced by the birth of a more eligible heir is known as heir presumptive.

A crown prince or hereditary prince is the 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 heiress apparent or, especially in earlier times, to the wife of the person styled crown prince.