This article introduces three princesses: Princess Elizabeth of Bohemia (1618-1680); her sister, Princess Sophie who became the Electress of Hanover (1630-1714); and Sophie's daughter, Sophie Charlotte, who became the first Queen of Prussia (1668-1705). After summarizing their common family background, the article presents, for each in turn, her biography and a discussion of her relation to philosophy. In each case their philosophical involvement stems from their friendships with the leading philosophers of their day; Princess Elizabeth was a friend of Descartes (...) while the Electress Sophie and Sophie Charlotte were friends of Leibniz. The article concludes that anyone who has made the acquaintance of the three princesses and has studied their interaction with their philosopher-friends will always see them as part of the history of modern philosophy. (shrink)