The physical, emotional, and social milestones of every girl's life: what we've lost and gained in the 21st century.

Caitlin Flanagan's essays about marriage, sex, and families have sparked national debates. Now she turns her attention to girls: the biological and cultural milestones for girls today, and how they shape a girl's sense of herself.

The transition from girl to woman is an experience that has changed radically over the generations: everything from how a girl learns about her period to how she expects to be treated by boys and men. Girls today observe these passages very differently, and yet the landmarks themselves have remained remarkably constant-proof, Flanagan believes, of their significance. In a world where protections of girls' privacy and personal freedom seem to disappear every day, the ultimate challenge modern parents face is finding a way to defend both.