Francine Pascal’s “Sweet Valley High” series of novels for older girls and young adults was one of the most protracted and successful series of the twentieth century. The romance-themed novels followed gorgeous and popular sixteen-year-old Elizabeth and Jessica Wakefi eld, twin sisters whose identical appearance belied their opposing personalities. In spite of its cool reception by teachers and librarians, the series developed a large fan base of young readers whose purchasing power pushed one volume of the series-a “super edition” called Perfect Summer-to a position on the New York Times list of best-selling paperback fi ction. While today this seems commonplace, the 1985 appearance of a teen paperback on the Times’ list marked the fi rst time in history that a young adult novel reached these best-seller heights. As the series grew in popularity, it spawned a television show and a number of spin-off book series: “Sweet Valley Twins” for younger independent readers, “Sweet Valley Kids,” for newly independent readers, and “Sweet Valley University,” for “graduates” of the high school series, are but three of even more sub-series associated with Pascal’s fi rst serial. “Sweet Valley High”’s association with a contested form of youth literature-series fi ction-and its relationship to the romance genre and popular reading practices has kept the series from critical consideration; however, the success and subsequent ubiquity of “Sweet Valley High” and Pascal’s literary domain deserves attention. An examination of the series’ history, content, structure and reception reveals the series to be an infl uential marketing and literary phenomenon and offers opportunities to interrogate the intersecting infl uences of history, audience positioning and readability that allowed “Sweet Valley High” to fl ourish.