Just as most people can remember exactly when, if ever, they had “the talk” with their parents, most millennial women can probably tell you about the first time they cracked open a slim little book called The Care and Keeping of You. Published in 1998 by American Girl, this trim, 104-page manual has taught millions of preteens — yes, it has sold more than 2 million copies — about personal hygiene and what to expect from puberty.

Its author, Valorie Lee Schaefer, finalized her book while she was on bed rest with her first daughter. Twenty-five years later, she took to Elle magazine to look back on the legacy of her wildly successful book.