The Danish Monarchy has existed for over 1000 years and is among the oldest in the world. The Danish Monarchy can be traced back to Gorm the Old (d. 958). The monarchy was originally elective, but in practice the choice was normally limited to the eldest son of the reigning monarch.
The democratic constitution of 5 June 1849 changed the monarchy's status from absolute to constitutional. The Act of Succession of 27 March 1953 allowed for the possibility of female monarch; that is what enabled HM The Queen to accede to the throne in 1972. Today Denmark has a constitutional monarchy, which means that the monarch cannot independently perform political acts.
Her Majesty's 40 years reign jubilee was celebrated in January 2012.