There is no right place. Do we begin with the story of boy meets girl (or girl buys sperm at a sperm bank?), the development of eggs and sperms, or the more traditional moment of fertilization (sperm fuses with egg)? No matter what point we choose, we start in the middle of the story of sex and gender; from there we can race forward, and end up looping back (Figure 2.1). For now, let’s start with a traditional framework, fill in some of the things we currently know about the biology of sex development, and then loop back to offer some interesting tidbits that complicate the basic story just a bit.