Ecological and evolutionary genetics span many disciplines and virtually all levels of biological investigation, from the genetic information itself to the principles governing the complex organization of living things. The ideas and informa tion generated by ecological and evolutionary genetics provide the substance for strong inferences on the origins, changes and patterns of structural and functional organization in bio logical communi ties. It is the coordination of these ideas and thoughts that will provide the answers to many fundamental questions in biology. There is no doubt that Drosophilids provide strong model systems amenable to experimental manipulation and useful for testing pertinent hypotheses in ecological and evolutionary genetics. The chapters in this volume represent efforts to use Drosophila species for such a purpose. The volume consists of a dedication to William B. Heed, followed by four major sections: Ecological Genetics, Habitat Selection, Biochemical Genetics and Molecular Evolution. Each section is introduced by a short statement, and each chapter has an independent summary. The chapters contain the sub stance of talks given at a joint Australia-US workshop held January 5-10, 1989 at the University of New England, New South Wales, Australia. We are indebted to the Division of International Programs of the National Science Foundation (USA) and to the Science and Technology Collaboration Section of the Department of Industry, Technology and Commerce (Australia) for the provi sion of financial support under the US/Australia Science and Technology Agreement. Many people contributed to the preparation of this volume.