1. Introduction
2. Sex differences in brain and behavior in context
3. Sex determination versus sex differentiation
4. Masculinization, feminization, and defeminization
5. Steroid hormones are potent modulators of brain development
6. Sex differences in the brain are established during a developmental sensitive window
7. Sex differences in reproductive physiology and behavior are coordinated
8. Steroids influence multiple endpoints via multiple mechanisms to organize the brain
9. Cellular mechanisms of steroid-mediated organization of the brain
10. Ultrasonic vocalizations differ in neonatal males and females because of a gene called FoxP2
11. Overcoming the hegemony of hormones: genes matter too
12. Winged messengers: lessons from birds and flies
13. Sexual differentiation of the primate brain
14. Sexual differentiation of the human brain
15. Imaging studies give insight into brain sex differences
16. Steroids and human brain development
17. The value of understanding the effect of sex on the developing brain.