Between XX and XY: Intersexuality and the Myth of Two Sexes - Gerald N. Callahan

An informative primer on gender and the trap of relying on outward appearance or chromosomal make-up.  People with a standing interest and knowledge base in gender studies and the complexities of gender may wish for more depth, however this is a fantastic book for readers new to the idea that XX and XY are not as reliable touchstones as we are often led to believe, and talks about a range of ways we are born that don't fit cleanly into binary 'male' or 'female'.