Book excerpt: Understanding how a multicellular animal develops from a single cell (the fertilized egg) poses one of the greatest challenges in biology today. Development from egg to adult involves the sequential expression of virtually the whole of an organism's genetic instructions both in the mother as she lays down developmental cues in the egg, and in the embryo itself. Most of our present information on the role of genes in development comes from the invertebrate fruit fly, Drosophila. The two authors of this text (amongst the foremost authorities in the world) follow the developmental process from fertilization through the primitive structural development of the body plan of the fly after cleavage into the differentiation of the variety of tissues, organs and body parts that together define the fly. The developmental processes are fully explained throughout the text in the modern language of molecular biology and genetics. This text represents the vital synthesis of the subject that many have been waiting for and it will enable many specific courses in developmental biology and molecular genetics to focus on it. It will appeali to 2nd and 3rd year students in these disciplines as well as in biochemistry, neurobiology and zoology. It will also have widespread appeal among researchers. Authored by one of the foremost authorities in the world. A unique synthesis of the developmental cycle of Drosophila - our major source of information on the role of genes in development. Designed to provide the basis of new courses in developmental biology and molecular genetics at senior undergraduate level. A lucid explanation in the modern language of the science.