Our purpose in this text is to place the natural history of marsupials within an evolutionary framework. We feel that a synthesis of this sort is warranted for four reasons. First, we freely admit that we are biased towards the view that the questions of greatest utility in ecological theory are those framed in an evolutionary context, and that we are thus concerned with the ways in which individuals in different environments enhance their survival and reproduction. This perspective has been applied to marsupial reproduction only occasionally. Second, most of the literature on marsupial ecology continues to be descriptive, its authors being motivated by the dearth of natural history data for most species. While this descriptive information is desperately needed, the absence of a comparative framework has led to the use of disparate and incomparable methods and this has hindered synthesis. Third, where evolutionary theory has been applied to marsupials, it has often been done unwisely, using assumptions now discarded by evolutionary biologists. Last, we believe that the unique mode of reproduction in marsupials affords an opportunity to examine a number of problems of general relevance. We show that behavioural and ecological convergence between marsupials and eutherians has been as frequent as morphological convergence.