Marsupials, the 'other' mammals, are found only in Australasia and the Americas. They are quite different from eutherian ('placental') mammals, as well they might be after 130 million years of separate evolution. They display a unique pattern of mammalian organization and development that is reflected by differences in their genomes. Here, we introduce marsupials as alternative (but not inferior!) mammals and summarize the state of knowledge of marsupial relationships, marsupial chromosomes, maps, genes and genetic regulatory systems. We shamelessly present the case for a Kangaroo Genome Project.