Learn More:
Kings (And Queens) Of The World: Where Monarchies Still Exist
http://www.npr.org/2011/04/26/135413612/kings-and-queens-of-the-world-where-monarchies-still-exist
"The British royal family never seems to lack attention from the press - witness the hype surrounding the marriage of Prince William, second in line to the throne, and Kate Middleton."

Meet the world's other 25 royal families
http://www.washingtonpost.com/blogs/worldviews/wp/2013/07/22/meet-the-worlds-other-25-royal-families/
"With all the attention around Britain's forthcoming Royal Baby, you'd think the U.K. had a monopoly on monarchs -- infant or otherwise."

CIA World Factbook: Government Type
https://www.cia.gov/library/publications/the-world-factbook/fields/2128.html

The International Commission and Association on Nobility
http://www.nobility-association.com/monarchytoday.htm

The Queen and the Commonwealth
http://www.royal.gov.uk/MonarchAndCommonwealth/Overview.aspx