As a book-obsessed ten-year-old in the early 1990s, I wrote Judy Blume a fan letter. I don't remember what it said—probably something about how much I loved her books, and how I wanted to be a writer too someday. But I still have her response. At the time, her form letter reply registered, to me, as a personal letter from a friend. I read it hanging on to every word, just as I did her books, which felt like mini lifelines as I clutched them late at night in my room or in the backseat of my mom’s car.

As fans know, Blume’s books approach weighty issues from an unapologetically girl-centered perspective. In her classic Are You There, God? It’s Me, Margaret, a pre-teen protagonist on the brink of getting her first period ponders the existence of God. In Just As Long As We’re Together, 9th grade Stephanie narrates the heartache of her parent’s divorce amid a breakup with her own best friend. In Deenie, a thirteen-year-old girl whose mom always wanted her to be a model, but who instead needs to wear a body brace for her scoliosis, navigates the nuances of disability, touching her "special spot" every night to escape the day's anxiety and fall asleep. And in Iggie’s House, a gum-smacking tomboy named Winnie confronts racism and white flight when her best friend moves away and a Black family moves into her old house (notably, Winnie is a white girl, but I appreciate Blume exploring race via white privilege rather than appropriating Black voices).

What I loved about Judy Blume growing up—and still love today—is that she takes young women seriously. From falling in love for the first time to navigating friendships to worrying about their bodies, she portrays young women’s lives, struggles, thoughts, and fears with the sincerity and care that they deserve. Blume turned 80 earlier this year, and throughout the last 50 years, her tender stories have carved out their own place in feminist history by translating the empowering messages of second-wave feminism to girls often considered too young to understand them.

Published in the early 1970s, some of Blume’s most well-known books offer a frankness around young women’s bodies and sexuality that was rare at the time of their publication, and even more so considering that they were written for young readers. Forever (1975), for instance, tells the story of high school senior Katherine who falls in love and decides to have sex for the first time. The book serves as a practical guide to sex, showing Katherine going to Planned Parenthood to get birth control, and describing her sexual encounters in pretty explicit detail (including a penis nicknamed Ralph). And, perhaps more importantly, it validates teens’ feelings and desires around sex, rather than shaming them.

Dr. Roberta Trites, a young adult literature critic and professor at the University of Illinois, agreed via email that Forever reads “at times like a self-help manual for having safe sex.” Its instructions, Trites noted, “include information about having a vaginal exam, how to get birth control, the anatomy of the penis, condom usage, information about premature ejaculation, venereal disease, impotence, sexual relations during menstruation, the breaking of the hymen, premarital pregnancy, and play-by-play directions for having intercourse.”

Five years before Forever’s publication, The Boston Women’s Health Collective published a 136-page booklet called Women and Their Bodies, which would later evolve into the groundbreaking Our Bodies, Ourselves. Packed with information empowering women to understand their reproductive health, Our Bodies doesn’t explicitly appear in Forever. But you can feel that Katherine inhabits a post-Our Bodies world, rich with its positive influence and with the ability of women to understand their own sexual agency.

Women and Their Bodies emphasizes that its lessons are meant to be spread around to women in various forms: “The papers in and of themselves are not very important. They should be viewed as a tool which stimulates discussion and action, which allows for new ideas and for change.” And just as its information was circulated among communities of forward-thinking women, Forever was passed clandestinely from teen girl to teen girl in the mid-70s and beyond,

serving much the same purpose.

Watch: The Riding Club Helping Disadvantaged Teens Aims Higher

Forever was accessible to teens in a way that a book like Our Bodies may not have been. And it’s illuminating even today. Blume’s depiction of a young woman enthusiastically consenting and enjoying a yes-means-yes model for sex feels particularly relevant to contemporary conversations around #MeToo, sexual assault, and coercion.

But Blume’s books are perhaps best known for their handling of puberty and menstruation. In her introduction to My Little Red Book, a 2009 anthology of first period stories by authors including Gloria Steinem and Erica Jong, editor Rachel Kauder Nalebuff writes that Blume’s Are You There God? It’s Me Margaret, “seems to be the bible for girls going through puberty.” What’s notable about Are You There God, as well as other Blume books on this subject, is not just that they dare to broach the subject of menstruation, but in particular how puberty is treated as unequivocally positive and exciting.

In her 2010 book New Blood: Third-Wave Feminism and the Politics of Menstruation, Dr. Chris Bobel writes about how attitudes toward periods began shifting amongst feminist activists and artists in the 1970s. She told me via email about various efforts during this era to raise consciousness around the safety of menstrual care products, break social taboos, and reframe “menstruation as an embodied source of power and pride.” Judy Chicago’s 1972 “Menstrual Bathroom” piece, which Bobel says aimed “to make visible the invisible—to lead people to confront the bodily process and examine their reactions to it,” is a vivid example of this activism, she notes. The same year that Are You There God came out, Germaine Greer even dared women to taste their own menstrual blood in The Female Eunuch: “If it makes you sick, you've got a long way to go, baby.”

With their thoughtful, complex young women narrators who we once saw ourselves in, Blume’s books remind us of how far we have come, and how far we have to go.

It was into this cultural moment that Are You There God was born, and its focus on period positivity can be seen as an extension of these ideas; a form of menstrual activism in its own right. Blume’s characters look forward to puberty, comparing themselves jealously to friends who have already begun menstruating. This eagerness feels downright utopian, given how menstruation is often treated in our culture—Bobel cites a 2004 study in her book finding that most women participants from all 34 countries surveyed reported negative emotions in reaction to their first period, while only a few mentioned positive reactions. This is a far cry from Margaret’s reaction of near euphoria, calling for her mom, crying with joy, and writing to God thanking him, finally sure of his existence: “I know you’re there God! I know you wouldn’t have missed this for anything!”

Trite says that, for many women of her generation, “Margaret was the first person who presented us with the idea that it was a good thing to menstruate because it is a mark of maturity and the potential to have children, not some sort of curse or taboo.”