As a teenager growing up in the 1970s, the sociologist Arlene Stein learned about homosexuality in a medical textbook she found at the public library. It delayed her process of coming out by at least a decade, she writes in her new book, “Unbound: Transgender Men and the Remaking of Identity.” She was horrified by those “scary pictures of naked people looking plaintively at the camera, arrayed like mug shots.”

This story hovers over her book, which delves into the lives of transgender men and other “gender dissidents.” It feels as if Stein has written this book imagining it might fall into the hands of those who need such a primer — much as she once did — and she wants to give them the fortification she yearned for. She depicts her subjects with warmth and respect, and strains to include as much as she can about the social, emotional, medical and psychological dimensions of transitioning. The result is frantically overstuffed but earnest, diligent and defiantly optimistic.

For a year Stein followed her four subjects — Parker, Lucas, Nadia and Ben — all patients at a Florida clinic world-famous for gender affirmation surgery, specifically chest masculinization. They are all young, affluent enough to afford the expensive surgery (the clinic doesn’t accept insurance) but a varied group in other ways. Parker is unabashed in his craving for male privilege. (“Yeah, I want to be a white American male property owner. Really, it’s a dream.”) Lucas has “huge problems with the idea of passing” as a man. Nadia wants top surgery but still identifies as a woman. Ben wants to be out as transgender and for people to know he was assigned female at birth. All report a sense of calm and joy after surgery, but some are uncomfortable with their sudden elevation in status when they present as men. People suddenly “remember my name,” Lucas reports.

“A younger generation of transgender men are prying open many of our assumptions about what it means to be men and women,” Stein writes. Old scripts are being discarded, including those about transitioning itself. Some of her subjects explain their desire to transition as a result of having been born in the “wrong body,” either because it feels accurate or out of necessity — “in order for patients to gain access to surgery and hormones,” Stein writes, “they must still use the language of suffering, pathology and cure.” Others express more expansive notions of gender, a desire to bend and break the binary.