So great is mammalian ecological and anatomical diversity that mating can take place under widely differing conditions depending upon which species is considered (e.g. in the water, on land, in the rainforest canopy, in burrows and on ice floes). This chapter focuses on the phylogenetic distribution of copulatory and associated behavioural traits throughout the Mammalia. The goal of this exercise is to determine, as far as possible, the degree of homology or convergent evolution that might exist between the various taxa, regarding their patterns of copulatory behaviour. As part of this exercise, it is important to consider the extent to which copulatory traits might have been moulded by ecological factors and by natural selection. This will pave the way for the discussions of the role played by sexual selection, in the next chapter.