Only 15 years ago, the term mammalian "genome" had a very different connotation than it does today. In a version of the Penguin Dictionary of Biology from that time, a genome was defined as "the set of chromosomes found in each nucleus of a given species." Those who studied the mammalian genome were called geneticists and they were classified primarily in two categories. Cytogeneticists examined chromosomes under the microscope, while transmission or "classical" geneticists followed the inheritance of genes with well-defined phenotypes--almost always gross morphological changes visible to the naked eye, isozymic differences, or immunologic differences. There were obvious limitations to the amount and types of "novel" information that could be uncovered with these techniques, and the study of mammalian genetics was often relegated to a secondary position, if it was taught at all, in many biology graduate programs in the United States and elsewhere. In fact, there seems to have been little reason for communication between mammalian geneticists and the molecular biologists of that period whose research was focused almost exclusively on prokaryotic and viral systems. In 1977 and 1978, the meaning connoted by mammalian genome changed drastically with the isolation of the first "genomic clones" and with the discovery of the first restriction fragment length polymorphisms. A new field was born with this marriage between molecular biology and mammalian genetics and, during the 13 years since, the amount of work published in this area has exploded exponentially, with significant ramifications in most other fields of biomedical research. The editors of this journal believe that this expansion will continue and that the coming years will represent the golden age of research on the mammalian genome. Our belief is bolstered by the strong interest shown in the "Human Genome Initiative" (which has come to include the mouse as a model mammalian system) by scientific communities in the United States, Europe, and Japan. Nevertheless, while these are exciting times for mammalian geneticists, those in the field are finding it increasingly difficult to assimilate the huge amount of information that has been and will continue to be generated by their colleagues. One serious problem is that while a number of broadbased journals are suitable for the publication of work in this area, there is no single journal devoted entirely to studies of the mammalian genome from a molecular and genetic perspective. We believe the need for such a journal is now critical, not only for the publication of original research articles, but also to serve as a focus and forum for the community of mammalian geneticists, and as a means for the organization and dissemination of genomic information. Mammalian Genome aims to accomplish these goals through (1) the publication of original papers that present new findings in all areas of mammalian genome research, including genomic organization and evolution, genetic and physical maps, comparative genomic studies, gene complexes, complex traits, animal models for human genetic disorders, new techniques, and DNA sequences and informatics as related to genome analysis; (2) the frequent publication of comprehensive summary reports on isolated genetic regions or gene systems (such as the report from the Mouse Chromosome 17 Committee in this issue); (3) the publication of reviews on topical areas of interest; and (4) its role as the official voice for the newly formed International Mammalian Genome Society (information concerning membership in this society is contained at the back of this issue).