People, chickens, giraffes, crickets, and maple trees all begin life as a fertilized egg, which we call a zygote. From this single cell, each organism proceeds to form its complex and distinct form. How can the products of a single cell be sorted out and properly located? The processes are not the same for all organisms, but they all work again and again. There are few biological processes more critical or more wondrous than embryonic development. Some of the wonders are explained in this chapter.