This chapter deals with some of the many prejudices surrounding the value of marsupials and monotremes as research organisms. It shows that most published research on mammalian biology actually only deals with placentals, and explains the historical background to the lack of scientific interest in monotremes and marsupials. Montremes are a complex mosaic of derived, ancestral and convergent traits, defying the perception that monotremes are a "primitive" representative of an ancestral mammal. The section on marsupials discusses a series of specific claims made about the evolutionary accomplishment of marsupials; in particular, the efficiency of marsupial reproduction, metabolism and development, the impact of development of morphological evolution, and the ability of marsupials to compete for niche space with placentals. In all cases, intriguing differences between monotremes, marsupials, and placentals serve to highlight the broad spectrum of mammalian evolution, rather than indicate a succession of evolutionary stages with differing evolutionary "merit."