This dissertation discusses the terms and contradictions of a genre I term the “maturation serial,” series of books that document the work of growing up properly of a central girl character. The maturation serial emerges in the postbellum nineteenth century as an enormously popular and commercially profitable genre that left large audiences of girls eager for more content about their favorite characters and women authors with incentive to provide. Girl characters growing up come up against the societal demands of sentimental women’s culture, which pits the terms of seriality against those of maturation. What emerges is an impossible genre, yet one that is endlessly generative. This project thus builds on longstanding work by theorists of various “impossible genres” and deploys work on sentimentality and feminism to inquire why this particular “impossible genre” has remained relatively unexplored and why the texts of the maturation serial have enjoyed such a long popularity. I look at three series by three North American authors of the late nineteenth and early twentieth centuries: the Anne of Green Gables series by L.M. Montgomery (1909-1939), the Little Women series by Louisa May Alcott (1868-1886), and the Elsie Dinsmore series by Martha Finley (1867-1905).