In recent years some very substantial advances have been made in our understanding of oogenesis as a result of studies on a relatively few, very diverse species of animals. In this lecture I will (1) outline normal oogenesis using an advanced insect, Drosophila melanogaster, as an example, (2) show how oogenesis can be dissected genetically by studying the ovarian pathologies of flies homozygous for various recessive, female sterile genes, and (3) discuss how estimates can be made of the fraction of the Drosophila genome devoted to oogenesis. Then I will describe studies on mutations that block vitello-genesis in Drosophila and indicate what they tell us about inter actions between the ovary, the fat body and the endocrine system. I will next discuss the evolutionary mechanisms that have been adopted in higher insects and amphibians to produce the prodigious quantities of ribosomes stored in oocytes. I will end with an account of the results of recent stuides on amphibian lampbrush chromosomes which show how messenger RNAs are transcribed during oogenesis.