The Bluebird Books is a series of novels popular with teenage girls in the 1910s and 1920s. The series was begun by L. Frank Baum using his Edith Van Dyne pseudonym, then continued by at least three others, all using the same pseudonym. Baum wrote the first four books in the series, possibly with help from his son, Harry Neal Baum, on the third. The fifth book is based on a fragment by Baum and written by an unknown author. The last five books were written by Emma Speed Sampson. The origin of the title is uncertain, but the books were all published in hardcover with blue cloth.