The ecological literature on marsupials is dominated by descriptive natural history, and there has hitherto been little attempt at either synthesis or evolutionary interpretation. This book attempts to provide such a synthesis, by drawing on both the descriptive data base and predictions from the burgeoning literature on behavioural and evolutionary ecology. It documents the excellent potential the study of marsupials provides for resolution of theoretical questions of general importance in biology. It does this in three ways. First, by describing the impressive diversity of marsupial life history strategies and trophic roles. Second, by careful comparison with the eutherians, the scope of the marsupial radiation is used to analyse the role of developmental constraints and adaptive radiation in determining the diversification of higher taxa. Lastly, it is suggested that the accessibility of marsupial young during their obligatory pouch life facilitates measurement, manipulation and assessment of kinship not possible in other mammalian groups. Further special topics include marsupial/plant mutualism, marsupial competition and the empirical uses of mammals with simple life histories.