Carolyn Keene is the pseudonym of the writers of the Nancy Drew and The Dana Girls mystery book series. The name "Carolyn Keene" is the invention of Edward Stratemeyer and the Stratemeyer Syndicate, which was known for packaging books for children. Ghost writer Mildred Wirt Benson was the first and primary writer of the Nancy Drew books before additional authors, including Edward Stratemeyer's daughter Harriet Adams, took over the mantle. The classic Nancy Drew series includes 78 books and the first, The Secret of the Old Clock, continues to be the most popular book. "Carolyn Keene" is also credited as writer to Nancy Drew spin-off book series River Heights and the Nancy Drew Notebooks.