Sietske de Haan (24 November 1889 – 31 October 1948), better known by her pen name Cissy van Marxveldt, was a Dutch writer of children's books.

Sietske de Haan was born on 24 November 1889 in Oranjewoud, a village in the northern province of Friesland in the Netherlands.

[1] De Haan embarked on her literary career by writing articles and stories for Dutch magazines, using the pseudonyms Cissy van Marxveldt, Betty Bierema en Ans Woud.

The series consists of five volumes: Van Marxvelt's Joop ter Heul novels for teenage girls had a notable influence on the writings of Anne Frank, who addressed her diary letters to an imaginary friend named Kitty.

Van Marxveldt also wrote many other young-adult books, of which Een zomerzotheid ("A Summer Folly") was a particular good seller, that made her affluent.