In this text one of the world's most eminent developmental biologists discusses some of the new insights into how genes control development. Walter Gehring describes in detail his contributions to the landmark discovery of the homeobox, a characterisitc DNA segment found in the genes of all higher organisms from the frutifly to humans, and he explains how this has provided the key to our modern understanding of development and evolution. The book thus becomes not only a discussion of genetics but also a description of the art of scientific investigation. Gehring begins his story by looking at the work of the many researchers who laid the foundation for the fields of molecular, cellular and developmental biology, providing vignettes of past and present investigators. He then describes his laboratory's hunt for the gene that caused odd mutations in the fruitfly - in which for example, antennae on the head were transformed into legs. He explains that researchers eventually found that the same master control genes that dictate the body plan in flies also pattern human bodies, limbs, hands, heart and brain. He illustrates the universality of the genetic control of development by describing the development of the eye; eyes as different as those of humans, squids, and flies, he shows, develop under the same master control gene.