"We give girls chocolate cake with vitamins" explains Pleasant T. Rowland, the creator of the American Girls books, summing up the philosophy behind the bestselling historical fiction series. The 1980s and 1990s have seen a proliferation of series books for girls—the Sweet Valley High series, the Baby-Sitters Club series, the American Girls series—which have sold millions of copies. Pleasant Company's American Girls Collection, a set of 36 books about six girls from different eras in American history, is among the leaders in this popular and profitable field. Preadolescent girls are a powerful demographic in 1990s publishing; girl power, it seems, represents a significant buying power. Series books for girls have frequently been dismissed both because they are popular reading and children's literature and because they are series books, which have historically been disdained by critics. Such books, however, have been an important and...