"Callahan does a good job of exploring intersex individuals, who are neither male nor female, and argues that they need to be accepted for what they are and not viewed as defective."  —Publishers Weekly

"Immunologist Callahan takes a fascinating look at the biology and human experience of intersexuality, a state in between male and female."  —Discover Magazine

"Callahan's writing style is both accessible and engaging; it reads more like creative non-fiction, a la Malcolm Gladwell."  —Ms. Magazine

"This is a fascinating, easily understandable journey into why we are born male or female and examines our age-old obsession with sex."  —Fort Collins Coloradoan

"There are lots of interesting nuggets here—for example, Callahan's description of biological sex as a spectrum, not a binary system."  —Double X

"The book is really beautifully written, highly accessible, and visionary in its own right."  —Feministing

"This book takes readers through an alphabet of gender and gender variations. Callahan shows readers that rather than either/or scenarios, there have always been variations; his book shatters our society's take on pink and blue."  —Advocate.com