A crown prince is a 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 heiress apparent or, especially in earlier times, to the wife of the person styled crown prince. The term "crown prince" has been used throughout history for the prince who is first-in-line to a throne and is expected to succeed, 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 or Prince of Asturias in the Kingdom of Spain). The term "crown prince" is not used in European monarchies where 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.

Crown princes are often involved in various activities and duties related to their position. For example, Crown Prince Haakon of Norway is patron of many national organizations, institutions, and foundations and is an honorary member of various associations and societies. He also participates in expeditions and attends to patronages and honorary tasks for more than 35 organizations and associations, which span a wide range of areas such as business, culture, sports, sustainability, and social purposes. Crown Prince Frederik of Denmark is also active in the defense and is the board chairman of Crown Prince Frederik and Crown Princess Mary’s Foundation, which supports humanitarian, social, and cultural purposes.